IMP Levels Research Articles

Quantitative Analysis of Purine Nucleotides Indicates That Purinosomes Increase de Novo Purine Biosynthesis

Enzymes in the de novo purine biosynthesis pathway are recruited to form a dynamic metabolic complex referred to as the purinosome. Previous studies have demonstrated that purinosome assembly responds to purine levels in culture medium. Purine-depleted medium or 2-dimethylamino-4,5,6,7-tetrabromo-1H-benzimidazole (DMAT) treatment stimulates the purinosome assembly in HeLa cells. Here, several metabolomic technologies were applied to quantify the static cellular levels of purine nucleotides and measure the de novo biosynthesis rate of IMP, AMP, and GMP. Direct comparison of purinosome-rich cells (cultured in purine-depleted medium) and normal cells showed a 3-fold increase in IMP concentration in purinosome-rich cells and similar levels of AMP, GMP, and ratios of AMP/GMP and ATP/ADP for both. In addition, a higher level of IMP was also observed in HeLa cells treated with DMAT. Furthermore, increases in the de novo IMP/AMP/GMP biosynthetic flux rate under purine-depleted condition were observed. The synthetic enzymes, adenylosuccinate synthase (ADSS) and inosine monophosphate dehydrogenase (IMPDH), downstream of IMP were also shown to be part of the purinosome. Collectively, these results provide further evidence that purinosome assembly is directly related to activated de novo purine biosynthesis, consistent with the functionality of the purinosome.

Effects of Various Salts on IMPase Activity and IMP Quantity in Coho Salmon, Oncorhynchus kisutch (Walbaum 1792), Salmonidae

Coho salmon, Oncorhynchus kisutch (Walbaum 1792), Salmonidae is a fast growing species that is reared for food worldwide. After harvest, coho salmon is often salted and stored. When a fish dies, adenosine triphosphate (ATP) is degraded in the muscles to inosinic acid (IMP), the taste component that gives the fish its flavour. During storage, IMP is degraded to non-taste components by the IMP-degrading enzyme (IMPase), resulting in a loss of flavour. Therefore, it is crucial to suppress IMPase activity in order to maintain IMP levels. In this study, IMPase activity was investigated at various pH levels and with salts used for storage of coho salmon, along with the resulting amount of IMP and changes in pH level. The results showed that the amount of IMP significantly decreased from 9.5 µmol·g -1 on day 0 to 4.6 µmol·g -1 on day 4 (p< 0.05) in fish stored at 4 o C in our laboratory but the pH level remained constant at 6.1±0.1. The enzyme activity was the highest at pH 6 and decreased sharply at pH 7-8. The salts that effectively maintained IMP in coho salmon were in the following order, MgSO4 and Na2SO4 at pH 4-5; MgCl2, CaCl2, MgSO4, and Na2SO4 at pH 6; and NaCl, CaCl2, and Na2SO4 at pH 7-8. These results indicated that the amount of IMP present after several days of storage was significantly higher with the addition of these salts.

Influence of sampling, storage, processing and optimal experimental conditions on adenylate energy charge in penaeid shrimp

Adenylate energy charge (AEC) has been used as a practical index of the physiological status and health in several disciplines, such as ecotoxicology and aquaculture. This study standardizes several procedures for AEC determination in penaeid shrimp that are very sensitive to sampling. We concluded that shrimp can be frozen in liquid nitrogen and then stored at -76?C for up to two years for further analysis, or freshly dissected and immediately homogenized in acid. Other cooling procedures, such as immersion in cold water or placing shrimp on ice for 15 min resulted in 50% and 73% decreases in ATP levels, and 9-fold and 10-fold increases in IMP levels, respectively. Optimal values of AEC (0.9) were obtained in shrimp recently transferred from ponds to indoor conditions, but decreased to 0.77 after one month in indoor tanks when stocked at high densities; the AEC re-established to 0.85 when the shrimps were transferred to optimal conditions (lower density and dark tanks). While the levels of arginine phosphate followed the same pattern, its levels did not fully re-establish. Comparison of different devices for sample homogenization indicated that a cryogenic ball mill mixer is the more suitable procedure.

사료 내 Nucleotides 첨가가 참돔P(agrus major)의 성장, 사료효율, 혈액성상 및 비특이적 면역반응에 미치는 영향

Two studies were conducted to investigate the effects of dietary nucleotides (NT) on the growth performance, hematological parameters, and innate immune responses of red seabream Pagrus major. In Expt I, six experimental diets were formulated: a control, four that contained each NT at a level of 0.15% (inosine monophosphate, IMP; adenosine monophosphate, AMP; guanosine monophosphate, GMP; and uridine monophosphate, UMP), and one with a 1:1:1:1 mixture of NTs (IMP, AMP, GMP, and UMP). In Expt II, five experimental diets were formulated that contained 0, 0.1, 0.2, 0.4, and 1.0% IMP (commercial product). Triplicate groups of juvenile (initial body weight 33.1 g) and growing (initial body weight 120 g) red seabream were fed one of the experimental diets to apparent satiation for 8 weeks in Expt I and 12 weeks in Expt II. In Expt I, fish fed diets with NT had higher growth performance than the control group. The nitroblue tetrazolium and lysozyme activities were higher in fish fed the mixed-NT diet, and lowest in the control group. In Expt II, the final body weight and feed utilization of fish fed the 0.1% IMP diet were significantly higher than those of fish fed the control or 1.0% IMP diets. Diet palatability was improved significantly when 0.1% IMP was added. The lysozyme activity was higher in fish fed diets with 0.4-1.0% than in the control group. These results suggest that supplementation of 0.15% IMP and Mixed-NTs in diet can enhance the growth and immune responses in juvenile red seabream. The optimum IMP level appears to be 0.2% in practical feed formulation for growing red seabream.

Selective inhibition of ATPase activity during contraction alters the activation of p38 MAP kinase isoforms in skeletal muscle

Muscle contractions strongly activate p38 MAP kinases, but the precise contraction-associated sarcoplasmic event(s) (e.g., force production, energetic demands, and/or calcium cycling) that activate these kinases are still unclear. We tested the hypothesis that during contraction the phosphorylation of p38 isoforms is sensitive to the increase in ATP demand relative to ATP supply. Energetic demands were inhibited using N-benzyl-p-toluene sulphonamide (BTS, type II actomyosin) and cyclopiazonic acid (CPA, SERCA). Extensor digitorum longus muscles from Swiss Webster mice were incubated in Ringer's solution (37°C) with or without inhibitors and then stimulated at 10 Hz for 15 min. Muscles were immediately freeze-clamped for metabolite and Western blot analysis. BTS and BTS + CPA treatment decreased force production by 85%, as measured by the tension time integral, while CPA alone potentiated force by 310%. In control muscles, contractions resulted in a 73% loss of ATP content and a concomitant sevenfold increase in IMP content, a measure of sustained energetic imbalance. BTS or CPA treatment lessened the loss of ATP, but BTS + CPA treatment completely eliminated the energetic imbalance since ATP and IMP levels were nearly equal to those of non-stimulated muscles. The independent inhibition of cytosolic ATPase activities had no effect on contraction-induced p38 MAPK phosphorylation, but combined treatment prevented the increase in phosphorylation of the γ isoform while the α/β isoforms unaffected. These observations suggest that an energetic signal may trigger phosphorylation of the p38γ isoform and also may explain how contractions differentially activate signaling pathways.

Metabolic engineering of the purine biosynthetic pathway in Corynebacterium glutamicum results in increased intracellular pool sizes of IMP and hypoxanthine

BackgroundPurine nucleotides exhibit various functions in cellular metabolism. Besides serving as building blocks for nucleic acid synthesis, they participate in signaling pathways and energy metabolism. Further, IMP and GMP represent industrially relevant biotechnological products used as flavor enhancing additives in food industry. Therefore, this work aimed towards the accumulation of IMP applying targeted genetic engineering of Corynebacterium glutamicum.ResultsBlocking of the degrading reactions towards AMP and GMP lead to a 45-fold increased intracellular IMP pool of 22 μmol gCDW-1. Deletion of the pgi gene encoding glucose 6-phosphate isomerase in combination with the deactivated AMP and GMP generating reactions, however, resulted in significantly decreased IMP pools (13 μmol gCDW-1). Targeted metabolite profiling of the purine biosynthetic pathway further revealed a metabolite shift towards the formation of the corresponding nucleobase hypoxanthine (102 μmol gCDW-1) derived from IMP degradation.ConclusionsThe purine biosynthetic pathway is strongly interconnected with various parts of the central metabolism and therefore tightly controlled. However, deleting degrading reactions from IMP to AMP and GMP significantly increased intracellular IMP levels. Due to the complexity of this pathway further degradation from IMP to the corresponding nucleobase drastically increased suggesting additional targets for future strain optimization.

Energy Metabolism during Repeated Sets of Leg Press Exercise Leading to Failure or Not

This investigation examined the influence of the number of repetitions per set on power output and muscle metabolism during leg press exercise. Six trained men (age 34±6 yr) randomly performed either 5 sets of 10 repetitions (10REP), or 10 sets of 5 repetitions (5REP) of bilateral leg press exercise, with the same initial load and rest intervals between sets. Muscle biopsies (vastus lateralis) were taken before the first set, and after the first and the final sets. Compared with 5REP, 10REP resulted in a markedly greater decrease (P<0.05) of the power output, muscle PCr and ATP content, and markedly higher (P<0.05) levels of muscle lactate and IMP. Significant correlations (P<0.01) were observed between changes in muscle PCr and muscle lactate (R2 = 0.46), between changes in muscle PCr and IMP (R2 = 0.44) as well as between changes in power output and changes in muscle ATP (R2 = 0.59) and lactate (R2 = 0.64) levels. Reducing the number of repetitions per set by 50% causes a lower disruption to the energy balance in the muscle. The correlations suggest that the changes in PCr and muscle lactate mainly occur simultaneously during exercise, whereas IMP only accumulates when PCr levels are low. The decrease in ATP stores may contribute to fatigue.

Monitoring of microbial metabolites and bacterial diversity in beef stored under different packaging conditions.

Beef chops were stored at 4°C under different conditions: in air (A), modified-atmosphere packaging (MAP), vacuum packaging (V), or bacteriocin-activated antimicrobial packaging (AV). After 0 to 45 days of storage, analyses were performed to determine loads of spoilage microorganisms, microbial metabolites (by solid-phase microextraction [SPME]-gas chromatography [GC]-mass spectrometry [MS] and proton nuclear magnetic resonance [(1)H NMR]), and microbial diversity (by PCR-denaturing gradient gel electrophoresis [DGGE] and pyrosequencing). The microbiological shelf life of meat increased with increasing selectivity of storage conditions. Culture-independent analysis by pyrosequencing of DNA extracted directly from meat showed that Brochothrix thermosphacta dominated during the early stages of storage in A and MAP, while Pseudomonas spp. took over during further storage in A. Many different bacteria, several of which are usually associated with soil rather than meat, were identified in V and AV; however, lactic acid bacteria (LAB) dominated during the late phases of storage, and Carnobacterium divergens was the most frequent microorganism in AV. Among the volatile metabolites, butanoic acid was associated with the growth of LAB under V and AV storage conditions, while acetoin was related to the other spoilage microbial groups and storage conditions. (1)H NMR analysis showed that storage in air was associated with decreases in lactate, glycogen, IMP, and ADP levels and with selective increases in levels of 3-methylindole, betaine, creatine, and other amino acids. The meat microbiota is significantly affected by storage conditions, and its changes during storage determine complex shifts in the metabolites produced, with a potential impact on meat quality.

Changes in purines concentration in the cerebrospinal fluid of patients experiencing pain: A case-control study

This study analyzes the relationship between extracellular purines and pain perception in humans. Cerebrospinal fluid (CSF) levels of purines and their metabolites were compared between patients displaying acute and/or chronic pain syndromes and control subjects. The CSF levels of IMP, inosine, guanosine and uric acid were significantly increased in the chronic pain group and correlated with pain severity (P<0.05). Patients displaying both chronic and acute pain presented similar changes in the CSF purines concentration (P<0.05). However, in the acute pain group, only CSF inosine and uric acid levels were significantly increased (P<0.05). These findings suggest that purines, in special inosine, guanosine and uric acid, are associated with the spinal mechanisms underlying nociception.

Post-Renal Transplant De Novo Non-Skin Malignancies in Mycophenolate Mofetil- and Calcineurin Inhibitor-Based Immunosuppression.

Abstract 1683Poster Board I-709Introduction- Post-transplant malignancy is one of the major complications of immunosuppression in kidney transplant recipients. Mycophenolate Mofetil(MMF) and Calcineurin inhibitors(CNI) based immunosuppression is a well established combination in clinical practice. MMF has an action on cell proliferation by inhibiting Inosine Mono Phosphate dehydrogenase. However, its antitumor properties have been constantly debated. It is shown to have some antiproliferative effects in leukemias and lymphomas with a decreased incidence of PTLD. This single center study evaluated the effect of combining mycophenolate mofetil (MMF) with calcineurin inhibitors on the incidence of de novo post-transplant non skin malignancies in renal transplant recipients. We also compared the incidence of solid versus liquid cancers.Patients and Methods- Six hundred and fifty seven (657) consecutive kidney and kidney/pancreas recipients transplanted between January 2000 and December 2005 were analyzed for post-transplant malignancies. Three hundred and sixty two (362) recipients were maintained on a calcineurin inhibitor and MMF combination. The incidence of neoplasm in this group was monitored till June 2009.All patients received induction therapy with basiliximab and methylprednisolone. Steroid therapy was discontinued after the second dose in the withdrawal group. In the steroid treated group oral prednisone was initiated on day 2 at 30 mg per day and rapidly tapered to 5 mg per day at one month and continued for the life of the graft. Maintenance therapy in all recipients included both, a calcineurin inhibitor and mycophenolate mofetil (MMF).All clinical acute rejections were confirmed by biopsy and treated with intravenous methylprednisolone. Steroid unresponsive rejections were treated with ThymoglobulinTable 1shows the demography in the CNI + MMF recipient groupRecipient demographyCalcineurin inhibitor/MMF groupNumber of recipients362Mean age in years53 ± 3Male gender196Deceased donor kidney recipients305Mean HLA antigen mismatch3.95 ± 2.6Pre-transplant malignancies0Number of recipients with rejection71Table 2Incidence and type of malignancies in calcineurin inhibitor + MMF groupType of cancerCalcineurin inhibitor/MMF groupTotal number of recipients362Post transplant lymphoproliferative disease1Hodgkin's lymphoma1Renal cell cancer6Lung cancer3Prostate cancer2Colon cancer2Breast cancer2Bladder cancer1Pancreatic cancer1Leukemia1Thyroid cancer1Total cancers21 (5.8%)ConclusionIn our study on CNI/MMF based immunosuppression in renal transplant patients, 5.8% developed various neoplasms. There was a lower incidence of hematologic- malignancies 3/362(0.8%) in comparison to solid organ neoplasm 18/362(4.97%). The incidence of PTLD was 0.27%, which is similar to other observational studies. This could partly be due to greater expression of Inosine Monophosphate, inhibited by MMF in malignant hematologic cells. Further multicenter analysis needs to be done to detect the incidence of liquid and solid neoplasms, correlating with intracellular IMP levels with MMF usage in renal transplant recipients. DisclosuresNo relevant conflicts of interest to declare.

정상돈육과 모의 열등돈육의 사후 초기 ATP 및 관련 뉴클레오타이드 함량 변화

Early postmortem ATP level is known as a good predictor of pork quality. Pork carcasses were divided into two; one was electrically stimulated (ES) to simulate poor quality pork and the other was left untreated and served as a control normal pork. Fractions of longissimus were excised from carcasses regularly for 2 hours after death and deep-frozen (-80C) until analyses. The ATP level of normal untreated control pork decreased from 5.00 to 2.04 μmole/g within 2 hours postmortem. The decrement of ATP was approximately 60% of its initial content. In the meantime, ES poor quality pork had a more drastic rate of ATP decrease. Electrical stimulation itself decreased ATP level from 4.70 to 3.50 μmole/g, by approximately 25%. ATP level of ES pork dropped to 1.71 μmole/g within 1 hour postmortem and was further plunged to 0.26 μmole/g and almost exhausted during the next hour. The level of IMP increased from 0.49 to 3.17 μmole/g and it became the dominant nucleotide within 2 hours postmortem. Electrical stimulation prompted the increase of IMP from 0.69 to 3.19 μmole/g and its level went up to 6.64 μmole/g within 2 hours postmortem. The level of ADP also decreased from 1.45 to 0.67 μmole/g for 2 hours after death and ES also accelerated ADP breakdown. The AMP levels were lower than those of other nucleotides and increased from 0.16 to 0.31 μmole/g within 2 hours postmortem. The increase of AMP was accelerated between 60 and 90 minutes after electrical stimulation. Early postmortem electrical stimulation prompted a drastic rate of changes in contents of 4 nucleotides during 2 hours postmortem. In the meantime, the ATP levels for ES poor quality pork were much lower than those of normal pork.

Cloning of immunodominant membrane protein genes of phytoplasmas and theirin plantaexpression

Phytoplasmas are plant pathogenic bacteria that cause devastating yield losses in diverse crops worldwide. Although the understanding of the pathogen biology is important in agriculture, the inability to culture phytoplasmas has hindered their full characterization. Previous studies demonstrated that immunodominant membrane proteins could be classified into three types, immunodominant membrane protein (Imp), immunodominant membrane protein A (IdpA), and antigenic membrane protein (Amp), and they are nonhomologous to each other. Here, cloning and sequencing of imp-containing genomic fragments were performed for several groups of phytoplasma including the aster yellows and rice yellow dwarf groups, for which an imp sequence has not previously been reported. Sequence comparison analysis revealed that Imps are highly variable among phytoplasmas, and clear positive selection was observed in several Imps, suggesting that Imp has important roles in host-phytoplasma interactions. As onion yellows (OY) phytoplasma was known to have Amp as the immunodominant membrane protein, the protein accumulation level of Imp in planta was measured compared with that of Amp. The resulting accumulation of Imp was calculated as approximately one-tenth that of Amp, being consistent with the immunodominant property of Amp in OY. It is suggested that an ancestral type of immunodominant membrane protein could be Imp, and subsequently the expression level of Amp or IdpA is increased in several phytoplasma groups.

Flavour formation in pork semimembranosus: Combination of pan-temperature and raw meat quality

Flavour development and overall eating quality of pork semimembranosus were investigated with regard to different raw meat qualities (feeding/fasting strategy; control/low glycogen level, gender; castrate/female, slaughter live-weight; 84kg/110kg) combined with frying temperature (150°C/240°C). It was further investigated whether the precursor levels of glycogen, IMP, inosine, and hypoxanthine in the raw meat were correlated to the raw meat quality and fried/grilled attributes. Pork schnitzels were fried on a pan (155°C) or grill–pan (240–250°C) to a core temperature of 70°C. Frying temperature was the one factor with greatest influence on the sensory attributes, and pan-grilled schnitzels had significantly higher scores in fried/grilled attributes regardless of meat quality compared to pan-fried schnitzels. Texture was not appreciably influenced by any treatment. There was no correlation between precursor levels and raw meat qualities or fried sensory attributes. Gender and slaughter live-weight had no pronounced influence on flavour and overall eating quality.

Environmental heat stress, hyperammonemia and nucleotide metabolism during intermittent exercise

This study investigated the influence of environmental heat stress on ammonia (NH3) accumulation in relation to nucleotide metabolism and fatigue during intermittent exercise. Eight males performed 40 min of intermittent exercise (15 s at 306+/-22 W alternating with 15 s of unloaded cycling) followed by five 15 s all-out sprints. Control trials were conducted in a 20 degrees C environment while heat stress trials were performed at an ambient temperature of 40 degrees C. Muscle biopsies and venous blood samples were obtained at rest, after 40 min of exercise and following the maximal sprints. Following exercise with heat stress, the core and muscle temperatures peaked at 39.5+/-0.2 and 40.2+/-0.2 degrees C to be approximately 1 degrees C higher (P<0.05) than the corresponding control values. Mean power output during the five maximal sprints was reduced from 618+/-12 W in control to 558+/-14 W during the heat stress trial (P<0.05). During the hot trial, plasma NH3 increased from 31+/-2 microM at rest to 93+/-6 at 40 min and 151+/-15 microM after the maximal sprints to be 34% higher than control (P<0.05). In contrast, plasma K+ and muscle H+ accumulation were lower (P<0.05) following the maximal sprints with heat stress compared to control, while muscle glycogen, CP, ATP and IMP levels were similar across trials. In conclusion, altered levels of "classical peripheral fatiguing agents" does apparently not explain the reduced capacity for performing repeated sprints following intermittent exercise in the heat, whereas the augmented systemic NH3 response may be a factor influencing fatigue during exercise with superimposed heat stress.

Relationships between hemodynamic parameters and myocardial energy and antioxidant status in heart transplantation

The relationships between high-energy phosphate levels, oxidative insult and mechanical function represent a key point in heart transplantation and related post-ischemic functional recovery. We evaluated myocardial purine compounds and glutathione antioxidant defence mechanism during 19 heart transplant operations. Heart biopsies were taken before harvesting on beating heart (t1), at the end of cold static preservation (t2) and 30 min after implantation and reperfusion (t3); perchloric extracts of the tissue were analyzed by capillary electrophoresis (CE). Correlation analyses were performed with hemodynamic parameters evaluated 90 min after aortic declamping (T90), 6 h following admission in intensive care unit (T6A) and 1 d post-operation (D1). We evidenced that AMP levels measured at T1 negatively correlate with both cardiac index (CI) and oxygen delivery index (DO2I) evaluated at T6A, respectively. The same behavior was evident plotting IMP levels measured at T3 with CI and DO2I evaluated at D1. After t2 the nucleotide/(nucleoside + base) ratio was in positive correlation with hemodynamic parameters at T6A. Energy charge and GSH/GSSG ratio measured before harvesting were in positive correlation with DO2I evaluated at T90. The present research shows that despite the complexity of the high-energy phosphate metabolism and that of the events associated to a clinical heart transplantation, there are some parameters that, besides reflecting the degree of myocardial preservation, also represents predictive parameters for the following organ functional recovery. It also suggests that heart preservation strategies should carefully take into account the sub-optimal nature of the donor heart at the time of procurement, through a broad spectrum of purine compound and glutathione antioxidant system measurements.

Effect of pre-slaughter physiological conditions on the oxidative stability of colour and lipid during chill storage of sliced, retail packed roast ham

Pre-slaughter physiological conditions (A serving as control, B subjected to treadmill exercise immediately prior to stunning, C epinephrine injection 15 h prior to slaughter, and D epinephrine injection 15 h prior to slaughter and subjected to treadmill exercise immediately before stunning) were found to significantly affect colour and lipid oxidation of sliced, retail packed roast ham, produced from nitrite-cured (78 ppm nitrite) M. Longissimus dorsi. The pre-slaughter treatment resulted in variations in the level of glycogen, lactate, ATP and IMP and pH development as monitored in Longissimus dorsi muscles, with the lowest ultimate pH (pH u) in muscles from non-epinephrine treated pigs (treatments A and B). The initial tristimulus L ∗-value and the L ∗-value during chill storage of sliced roast ham packed in laminates with low or with very low oxygen transmission rate (OTR=40 and <0.5 cm 3/m 2/atm/24 h, respectively) were significantly affected by treatment, although the effect of the treatments was different during storage for 28 days (interaction between treatment and storage time). Roast ham from treatments A and B generally had a paler appearance (higher L ∗-values) than from treatments C and D. No differences in the initial tristimulus a ∗-values (redness) were found. During chill storage, a pronounced colour fading (decrease in a ∗-values) was seen for laminate with low OTR, with a tendency of better colour stability for treatment C than A, but with no differences for the other treatments. For laminates with very low OTR, the cured meat pigment was stable with no decreases in a ∗-values during storage. Lipid oxidation (thiobarbituric acid reactive substances, TBARS) in products in laminates with low OTR increased during storage and was significantly higher for roast ham from non-epinephrine treated pigs (A and B) than for ham from epinephrine-treated pigs (C and D). Statistical analysis relating pH and the level of glycogen, lactate, creatine phosphate, ATP and IMP in the individual pigs to the product quality parameters revealed that the ultimate level of lactate was the most important single parameter affecting product quality. After 28 days of chill storage, roast ham from pigs subjected to treatments C and D were more likely to support bacterial growth than from treatments A and B. In conclusion, the results show that pre-slaughter physiological conditions are of importance for chemical as well as for microbiological changes in retail stored roast ham.

Li+ Induces Hypertrophy and Down Regulation of Myo-Inositol Monophosphatase in Tomato

Lithium (Li + ) is known to disrupt the development of several different organisms, presumably through the inhibition of Li + -sensitive enzymes such as the myo-inositol monophosphatase (IMP) enzyme. In animal cells, decreases in IMP activity result in down regulation of phosphatidylinositol signaling, which can alter development. We characterized the effects of Li + on germinating tomato seedlings. It was found that an increase in cell size, termed hypertrophy, results from application of LiCI but not other tested salts. Hypertrophic growth was found to consist of greatly enlarged cells that originate from within the cortex of the seedling stem. Measurements of 44 elements within the hypertrophic tissue indicated that only Li + accumulated in a pattern consistent with the observed alterations in stem growth. We found that in response to Li + , the IMP activity and levels of the three isoforms of IMP were down regulated. These results suggest that down regulation of IMP via Li + is involved in the process of hypertrophic growth.

Muscle function during fatigue in myoadenylate deaminase-deficient Dutch subjects.

Myoadenylate deaminase (MAD) is an enzyme active in skeletal muscle, probably during exercise of moderate intensity but certainly during vigorous exercise, when the deamination of AMP leads to increased levels of IMP and ammonia. There is controversy about the clinical significance of MAD deficiency. The main objective of the present study was to investigate the extent to which genetically confirmed MAD deficiency affects muscle function under conditions of maximal short-term electrically induced activation. The left hand was immobilized and adductor pollicis muscle function was investigated. To exclude the influence of central factors, such as the patient's motivation, the ulnar nerve was maximally electrically activated and force output was measured at the thumb. Sixty rapid shortening contractions resulted in a decrease of maximal power to 34.2+/-5.4% and 33.3+/-6.3% (means+/-S.D.) of the values for unfatigued muscle in the control and MAD-deficient subjects respectively (P>0.05; n=7). Maximal isometric forces and shortening velocities did not differ between groups in unfatigued, fatigued or recovered muscle. None of the subjects experienced exercise-related muscle aches or cramps. In conclusion, MAD deficiency does not appear to affect adductor pollicis muscle force, shortening velocity and relaxation, either during or after maximal short-term activation.

Muscle function during fatigue in myoadenylate deaminase-deficient Dutch subjects

Myoadenylate deaminase (MAD) is an enzyme active in skeletal muscle, probably during exercise of moderate intensity but certainly during vigorous exercise, when the deamination of AMP leads to increased levels of IMP and ammonia. There is controversy about the clinical significance of MAD deficiency. The main objective of the present study was to investigate the extent to which genetically confirmed MAD deficiency affects muscle function under conditions of maximal short-term electrically induced activation. The left hand was immobilized and adductor pollicis muscle function was investigated. To exclude the influence of central factors, such as the patient's motivation, the ulnar nerve was maximally electrically activated and force output was measured at the thumb. Sixty rapid shortening contractions resulted in a decrease of maximal power to 34.2±5.4% and 33.3±6.3% (means±S.D.) of the values for unfatigued muscle in the control and MAD-deficient subjects respectively (P &gt; 0.05; n = 7). Maximal isometric forces and shortening velocities did not differ between groups in unfatigued, fatigued or recovered muscle. None of the subjects experienced exercise-related muscle aches or cramps. In conclusion, MAD deficiency does not appear to affect adductor pollicis muscle force, shortening velocity and relaxation, either during or after maximal short-term activation.

Energy metabolism and lipid peroxidation of human erythrocytes as a function of increased oxidative stress.

To study the influence of oxidative stress on energy metabolism and lipid peroxidation in erythrocytes, cells were incubated with increasing concentrations (0.5-10 mM) of hydrogen peroxide for 1 h at 37 degrees C and the main substances of energy metabolism (ATP, AMP, GTP and IMP) and one index of lipid peroxidation (malondialdehyde) were determined by HPLC on cell extracts. Using the same incubation conditions, the activity of AMP-deaminase was also determined. Under nonhaemolysing conditions (at up to 4 mM H2O2), oxidative stress produced, starting from 1 mM H2O2, progressive ATP depletion and a net decrease in the intracellular sum of adenine nucleotides (ATP + ADP + AMP), which were not paralleled by AMP formation. Concomitantly, the IMP level increased by up to 20-fold with respect to the value determined in control erythrocytes, when cells were challenged with the highest nonhaemolysing H2O2 concentration (4 mM). Efflux of inosine, hypoxanthine, xanthine and uric acid towards the extracellular medium was observed. The metabolic imbalance of erythrocytes following oxidative stress was due to a dramatic and unexpected activation of AMP-deaminase (a twofold increase of activity with respect to controls) that was already evident at the lowest dose of H2O2 used; this enzymatic activity increased with increasing H2O2 in the medium, and reached its maximum at 4 mM H2O2-treated erythrocytes (10-fold higher activity than controls). Generation of malondialdehyde was strictly related to the dose of H2O2, being detectable at the lowest H2O2 concentration and increasing without appreciable haemolysis up to 4 mM H2O2. Besides demonstrating a close relationship between lipid peroxidation and haemolysis, these data suggest that glycolytic enzymes are moderately affected by oxygen radical action and strongly indicate, in the change of AMP-deaminase activity, a highly sensitive enzymatic site responsible for a profound modification of erythrocyte energy metabolism during oxidative stress.