ME Activity Research Articles

Modelling NADH turnover in plant mitochondria.

NADH is central to the functioning of mitochondrial respiration. It is produced by enzymes in, or associated with, the tricarboxylic acid cycle in the matrix, and it is oxidized by two respiratory chain enzymes in the inner membrane, the rotenone-sensitive complex I and the rotenone-insensitive internal NADH dehydrogenase (ND(in)). A simplified kinetic model for NADH turnover in the matrix of plant mitochondria is presented. Only the two main NADH-producing enzymes, NAD-malate dehydrogenase [EC 1.1.1.37] (MDH) and NAD-malic enzyme [EC 1.1.1.39] (ME), are considered. This model reproduces the complex behaviour of malate oxidation by isolated mitochondria in response to additions of ADP (state 3/state 4), NAD(+) and/or rotenone, as well as to changes in pH. It is found that MDH always operates at or close to equilibrium. Changes in the activity of complex I, ND(in), or ME are predicted to cause clear changes in the pattern of malate oxidation. In general, the model predicts high sensitivity to changes in the ME activity. In contrast, MDH activity can be reduced 100-fold without detectable changes in malate oxidation. It is demonstrated that it is not the high activity, but the equilibrium properties of MDH that are important for the redox-buffering function of MDH in the mitochondrial matrix. Binding of NAD(+) and NADH in the matrix reduces the concentrations of free NAD(+) and NADH, depending on the concentration of binding sites and the binding strength. On the basis of the modelling results it is estimated that a significant proportion of the mitochondrial NAD is bound.

Isozyme analysis of Taenia solium isolates from Mexico and Colombia.

Mexican and Colombian Taenia solium cysticerci and some species of Taenia adults were assayed using cellulose acetate electrophoresis to distinguish between isolates. Isozyme patterns for ARK, GOT, G3PD, GPI, and MPI were identical in all cysticerci suggesting homozygotic profiles. G6PD and MDH showed different patterns between Mexican and Colombian cysticerci, suggesting regional differences. ME activity was mainly detected in the adult stage suggesting that this enzyme is active in anaerobic environment, while MDH, detected in cysticerci, could be related to an environment that contains oxygen. Finally, the species of taeniid adults analyzed showed different patterns among them.

Methimzole and thyroid hormone replacement in broilers

Seven-day-old chickens were fed diets containing 18% crude protein+0 or 1 g methimazole/kg to produce either euthyroid or hypothyroid groups of birds at 28 days of age. These two groups were then offered diets containing either 0 or 1 mg triiodothyronine (T 3)/kg diet. Birds were sampled at 0, 2, 5, and 8 days following the onset of the T 3 treatment. Measurements taken at these intervals included in vitro hepatic lipogenesis (IVL), growth and feed consumption, hepatic enzyme activities (malic enzyme, ME; isocitrate dehydrogenase, ICD; and aspartate amino transferase, AAT), plasma hormones (T 3; thyroxine, T 4; insulin like growth factors I, IGF-I; and insulin like growth factors II, IGF-II) and metabolites (glucose; fatty acids, NEFA; triglyerides; uric acid). Hypothyroidism decreased IVL and ME at 28 days of age; however, T 3 supplementation for 2 days restored both IVL and ME. Paradoxically, continuing T 3 replenishment for an additional 3–6 days decreased IVL without affecting ME activity. In contrast, supplemental T 3 decreased IVL in euthyroid birds, regardless of the dosing interval, but had no effect on ME activity. Methimazole decreased plasma T 3, T 4, uric acid, and IGF-I, but did not affect IGF-II at 28 days. Giving T 3 to birds previously on methimazole increased plasma IGF-I as did feeding a control diet. Supplemental T 3 increased NEFA in both euthyroid and hypothyroid birds, but only for a short period following the initiation of supplementation (2 days post-supplementation). These data may help to explain some of the apparent reported dichotomies in lipid metabolism elicited by changes in the thyroid state of animals. In addition, most metabolic changes in response to feeding T 3 occurred within 2–5 days, suggesting that changes in intermediary metabolism preceded morphological changes. In conclusion, the thyroid state of the animal will determine responses to exogenous T 3.

Thermodynamic Properties of Me2Ni17(Me = Sm, Dy, and Yb) Intermetallics by Solid Electrolyte Cells under Effusion Conditions

The purpose of this work is to contribute to rare earth/3d metal thermodynamics of systems not experimentally determined prior to this research. The thermodynamics of the Ni-rich phase, Me 2 Ni 1 7 , in the binary systems Me-Ni, with Me = Sm, Dy, and Yb, has been studied in the temperature range from 900 to 1200 K by a new experimental setup based on solid-state galvanic cells with CaF 2 single crystal as the solid electrolyte. This is particularly useful when the vapor pressure of one of the components of the electrochemical cell is high at the working temperature. The electromotive force method has been adopted to obtain the thermodynamic properties of the intermetallics under investigation. Their Δ f H 0 T values have been found to be -14.6 ′ 0.5, -18.5 ′ 0.1, and -17.0 ′ 0.1 kJ/mol atoms, respectively, for Sm 2 Ni 1 7 and Dy 2 Ni 1 7 at T = 298 K and Yb 2 Ni 1 7 at T = 990 K. These values agree well with the calculated values obtained through the Miedema model. Values of the activity of Me in the Ni solid solution in thermodynamic equilibrium with the respective Me 2 Ni 1 7 phase were calculated at 1000 K to be 6.8 x 10 - 1 0 , 4.8 x 10 - 1 0 , and 1.5 x 10 - 1 0 , respectively, for Sm, Dy, and Yb. The activity against the Me atomic volume was also investigated together with the physical meaning of the partial excess free energy change of the Ni solid solution.

Role of hepatic lipogenesis in the susceptibility to fatty liver in the goose ( Anser anser)

In response to overfeeding, the Landes goose develops a fatty liver that is twice as large as that of the Poland goose, despite similar food intake. The role of hepatic lipogenesis in the genetic susceptibility to fatty liver was assessed in male overfed geese of the two breeds. For a similar hepatic protein content, total activities of malic enzyme, glucose-6-phosphate dehydrogenase, acetyl-Coa-carboxylase and fatty acid synthase, and specific activity and mRNA level of malic enzyme were about two-fold higher in the Landes goose. In the Poland goose, the weight of the fatty liver was correlated positively with the specific activity of ME and the VLDL concentration, which was not the case in the Landes breed. These results show that: (1) hepatic lipogenesis remains very active until the end of the overfeeding period; (2) the pentose-phosphate pathway may function in birds, contrary to what is assumed usually; (3) the level of hepatic lipogenesis is a major factor in the susceptibility to hepatic steatosis in different breeds of geese; and (4) ME activity may be a limiting factor of lipid synthesis in the less susceptible Poland breed.

ChemInform Abstract: Remarkable Catalytic Activity of Me3Ga in the Alkylation of Hetero‐Substituted Epoxides with Alkynyllithiums.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The tyrosine phosphatase SHP-1 is a negative regulator of osteoclastogenesis and osteoclast resorbing activity: increased resorption and osteopenia in mev/mev mutant mice

Naturally occuring inactivating mutations of the Src homology 2 (SH2) domain-containing tyrosine phosphatase 1 (SHP-1) in mice give rise to the motheaten ( me) phenotype. me/me mice have multiple hematopoietic abnormalities, suggesting that this phosphatase plays an important role in hematopoiesis. SHP-1 binds to and is activated by several hematopoietic surface receptors, including the colony-stimulating factor type 1 receptor. We have examined the role of SHP-1 in osteoclastogenesis and osteoclast function using mice with the viable motheaten ( me v /me v ) mutation, which has markedly decreased SHP-1 activity. Histomorphometric analysis of 6-week-old me v /me v mice and control littermates showed a marked osteopenia with an increase in bone resorption indices. The number of formed osteoclast-like cells (OCLs) in cocultures of me v /me v hematopoietic cells with normal osteoblasts was significantly increased. In contrast, the number of OCLs formed in the coculture of normal bone marrow cells with the me v /me v osteoblasts was not significantly different from controls. The bone-resorbing activity of me v /me v OCLs and authentic osteoclasts was also found to be increased. Finally, Western blotting of proteins from me v /me v and control OCLs revealed an overall increase in tyrosine phosphorylation in the me v /me v lysates. These in vivo and in vitro results suggest that SHP-1 is a negative regulator of bone resorption, affecting both the formation and the function of osteoclasts.

The role of malic enzyme in the regulation of lipid accumulation in filamentous fungi.

The hypothesis is advanced that NADP(+)-malic enzyme (ME; EC 1.1.1.40) is an important activity in regulating the extent of lipid accumulation in filamentous fungi. In Mucor circinelloides, a fungus capable of accumulating only 25% (w/w, dry wt) lipid, even under the most propitious conditions, ME disappears 15-20 h after nitrogen exhaustion, coincident with the cessation of lipid accumulation. In contrast, ME in Mortierella alpina, a fungus capable of accumulating 50% (w/w, dry wt) lipid, remains active for over 60 h after N-exhaustion during which time lipid accumulation continues. No other enzyme activity studied, including the lipogenic enzymes acetyl-CoA carboxylase, fatty acid synthase, diacyglycerol acyltransferase, ATP: citrate lyase and the NADPH-generating enzymes glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase and NADP+:isocitrate dehydrogenase, demonstrated any correlation with the accumulation of storage lipid in either fungus. Full activity of ME is restored in Mr. circinelloides within 4 h by adding NH4+ to the cultures, but this is prevented by adding cycloheximide as an inhibitor of protein synthesis. This suggests that the decrease in ME activity occurs due to down-regulation of the ME gene.

Citric-Acid Cycle Key Enzyme Activities during In vitro Growth and Metacyclogenesis of Leishmania infantum Promastigotes

The activities of 5 key regulatory enzymes in most energetic systems, namely citrate synthase (EC 4.1.3.7, CS), NADP-specific isocitrate dehydrogenase (EC 1.1.1.42, ICDH), succinate dehydrogenase (EC 1.3.99.1, SDH), L-malate dehydrogenase (EC 1.1.1.37, MDH), and decarboxylating malic enzyme (EC 1.1.1.40, ME), were measured during the growth and metacyclogenesis of a cutaneous (CL) and a visceral (VL) strain of Leishmania infantum. As occurs with other Leishmania species, infective promastigotes were present along all phases of growth, but their percentages were higher at the early stationary phase for VL and the end of the same phase for CL. High CS and SDH activities were detected in both strains, as compared with other trypanosomatids, bringing more evidence for an actively functional citric-acid cycle in L. infantum. Both strains showed higher levels of CS, ICDH, and MDH and lower SDH and ME activities when more metacyclic promastigotes were present, but in VL these changes paralleled an increase in glucose consumption, whereas in CL these changes coincided with an NH3 hyperproduction. This suggests that the energy metabolism during L. infantum growth and metacyclogenesis is affected by regulated enzymes that probably respond to changes in the culture medium in the levels of glucose and amino acids.

The Effect of GH and IGF-I on Preadipocytes from Large White and Meishan Pigs in Primary Culture

Proliferation and differentiation of preadipocytes from 7-day-old Large White (LW) and Meishan (MS) pigs were studied in primary culture. The effects of porcine GH (pGH) and IGF-I as well as the expression of GH (GHR) and IGF-I (IGF-IR) receptors mRNA were examined. Preadipocytes were exposed to serum-supplemented and serum-free medium to determine proliferation and differentiation, respectively. Proliferation was higher in MS than in LW pigs. Treatment with pGH (2 nM) or IGF-I (10 nM) resulted in a similar decrease in proliferation in LW and MS pigs. Parameters assessing differentiation and the effects of pGH and IGF-I on differentiation did not differ between the two breeds. The percentage of differentiating cells and LPL and ME activities were markedly reduced by pGH. IGF-I did not reduce differentiation significantly. Both GHR and IGF-IR mRNA were expressed in adipose tissue, adipocytes, preadipocytes, and 6-day-cultured cells from LW and MS pigs. The similar action of pGH and IGF-I on preadipocyte proliferation and differentiation, associated with the similar expression of GHR and IGF-IR mRNA in LW and MS pigs, suggests that the GH/IGF-I axis is not impaired in MS pigs. The difference in preadipocyte proliferation observed between LW and MS pigs could account for their adiposity difference.

Energizing Your Teaching: Developing a Community of Learning

This paper is based on comments made in a presentation at the 1998 Annual Meeting of the American Accounting Association. Dennis M. Hanno is the Associate Dean for Undergraduate Matters at the University of Massachusetts Amherst. INTRODUCTION Teaching is my passion, and it is a passion that energizes every aspect of my role as a faculty member. It helps to motivate my research because I know that new knowledge will be created and then, through teaching, shared with my students and others. In addition, outreach and service activities provide me with opportunities to teach more people than the students in my classroom, and to teach in different ways and in varied forums. Talking and writing about teaching is also an enjoyable and fruitful activity for me. Palmer (1993) argues that continuing, thoughtful conversation about teaching is essential to creating an environment where good teaching can flourish. I concur with his belief that “the growth of any skill depends heavily on honest dialogue among those who are doing it.” Faculty often labor in a private world of teaching, and this solitude can discourage even the most adventurous teacher from discovering and trying new approaches. We are fortunate as accounting educators to have a number of forums for active discussion and sharing of ideas about teaching, and my active involvement in this dialogue also helps to energize my teaching activities. Each of us brings different skills and a unique background to the classroom, and we are all faced with the unique environment created by our academic institutions and students. As accounting educators, we also may be involved in teaching a wide range of subject matter. I realize that as a result of these differences, the tips and techniques that I use to energize my own teaching, or to motivate my students, may not be effective for others.1 However, I believe there are certain common themes and guiding principles that underlie what we all do. In reflecting on how I stay energized, I believe it

The isolation and characterisation of a mutant of the C 4 plant Amaranthus edulis deficient in NAD-malic enzyme activity

A mutant of Amaranthus edulis (Speg.) lacking activity of the C4 leaf form of NAD-malic enzyme (ME; EC 1.1.1.39) has been isolated. Homozygous mutant (5% wild-type ME activity) and heterozygous (50% wild-type ME activity) F2 plants were shown to contain both the α and β NAD-ME subunits in similar amounts to those detected in the wild-type leaves. The rate of photosynthetic CO2 assimilation was reduced in the homozygous mutant to 5% of that observed for the wild-type leaves. Other C4 enzymes were not down-regulated in the mutant plants. There was little difference in photosynthetic rate of the heterozygous plants compared to the wild-type, suggesting that NAD-ME exerts little control over the rate of C4 photosynthesis, and that in the wild-type the enzyme has a very low control coefficient. The activity loss in the heterozygote may therefore be compensated by regulatory mechanisms that increase the activity of the enzyme in vivo. Data for bundle-sheath strands indicated that although the homozygous mutants were able to oxidise malate via the Krebs cycle, they were unable to convert malate to pyruvate and alanine via NAD-ME.

Hydrogen evolution and hydrogen sorption on amorphous smooth MeP( x) (MeNi, Co and FeNi) electrodes

Hydrogen evolution reaction (HER) was studied on amorphous CoP( x), NiP( x) and FeNiP( x) electrodes, prepared by an electrolytic deposition. The activities of Ni and CoP( x) electrodes prepared at room temperature are nearly equivalent, those of FeNiP( x) are somewhat lower. Alloys prepared by the electrodeposition at room temperature are very active for the HER, while those prepared at elevated temperatures 80–90 °C are less active. It has been proved that the high activity of MeP( x) electrodes is caused by dissolved hydrogen in the amorphous layer in the course of the electrodeposition.

Nickel and cadmium toxicity and enzymatic activity in nitolerant and non-tolerant populations of Silene italica Pers.

Ni 2+ and Cd 2+ toxicity and effects on the activity of glucose-6-phosphate dehydrogenase (G6PDH, EC 1.1.1.49), glutamate dehydrogenase (GDH, EC 1.4.1.2), malic enzyme (ME, EC 1.1.1.40), and isocitrate dehydrogenase (ICDH, EC 1.1.1.42) were evaluated in two populations of Silene italica , a Ni-tolerant ecotype from serpentine soils very low in Cd 2+ , and a population sensitive to both Ni 2+ and Cd2+ and originating from a normal soil. The Ni-tolerant population is more tolerant to both metals than the ecotype originating from a normal soil. Both Ni2+ and Cd 2+ assimilation induce a stronger increase of G6PDH, GDH, and ICDH activity in the Ni-tolerant than in the Ni-sensitive population. In the Ni-tolerant population Cd 2+ stimulates the activity of ME, GDH, and G6PDH to a greater extent than Ni 2+ does. Our results suggest that the tolerant population reacts better than the sensitive one to the toxic metal concentrations; the effects on the enzyme activities described may be involved in the response to metal stress conditions.

Metabolic enzyme activities in larvae of the African catfish, Clarias gariepinus: changes in relation to age and nutrition

The influence of ontogeny and nutrition on metabolic enzyme activities in larvae of the African catfish, Clarias gariepinus, was studied. After start of exogenous feeding, the larvae were reared for 10 days under three different nutritional conditions: Artemia nauplii, a dry starter diet, and starvation. The live feed gave the best growth (96 mg within 10 days) whereas the dry diet resulted in low growth (33 mg). This growth difference was reflected in larval RNA and DNA concentrations, but not in the levels of soluble protein. Enzymes representing the following aspects of metabolism have been analysed: NADPH generation (G6PDH, ME), glycolysis (PFK, PK), gluconeogenesis (FDPase), amino acid catabolism (GOT, GPT) and oxidative catabolism (CS). All enzymes were present from the start of exogenous feeding onwards, but their maximum specific activities displayed different developmental patterns. In catfish larvae fed on Artemia, G6PDH and ME activities steadily increased with age and weight of the larvae. CS levels remained, after an immediate enhancement upon onset of exogenous feeding, on a rather stable plateau. The amino acid-degrading enzymes GOT and GPT showed maximum levels at days 3-5 of feeding or at a body weight of 10-20 mg, but decreased thereafter. Activities of PFK, PK and FDPase showed low initial levels, and increased significantly with age and size. Based on the ontogenetic patterns of metabolic enzymes, in C. gariepinus larvae an early and a late developmental phase can be distinguished. During the early phase, the glycolytic and gluconeogenetic capacities are low, whereas they are enforced during the later phase. The oxidative capacity is high both during the early and the late phase. The metabolic changes in catfish development coincide with other major ontogenetic events, e.g., alterations of muscle organization, gill morphology, respiration and stomach structure and function. Rearing catfish larvae on a dry diet instead of Artemia partly altered the developmental pattern described: The ontogenetic elevation of CS, PFK and FDPase was delayed and the early peak in GOT and GPT activities was not realized. Particularly during the early developmental phase, the enzyme behaviour of the larvae fed on dry food was similar to that of starved larvae.

The effect of gamma-hexachlorocyclohexane (lindane) on the activities of liver lipogenic enzymes and on serum lipids in rats.

The effect of dietary gamma-hexachlorocyclohexane (lindane) (50-350 ppm, 0.17-1.19 mumol/kg chow) on the activity of enzymes of lipogenesis, viz., fatty acid synthase (FAS; EC 2.3.1.85), citrate cleavage enzyme (CCE; EC 4.1.3.8), malic enzyme (ME; EC 1.1.1.40), glucose-6-phosphate dehydrogenase (G6PDH; EC 1.1.1.49) and 6-phosphogluconate dehydrogenase (PGDH; EC 1.1.1.44), and on serum lipid levels, was investigated in livers of 35-day-old male Wistar rats. Lindane (150 ppm) caused a substantial decline of enzyme activities within the first 24 h of treatment. The decrease was transient, however, and enzyme activities subsequently recovered despite continuation of lindane feeding. The recovery of enzyme activities was comparatively fast in the case of ME, G6PDH and PGDH, but very slow with FAS and CCE. Activities of lipogenic enzymes decrease when animals are starved, and increase much beyond prestarvation levels upon subsequent refeeding. Lindane in the refeeding diet blunted this overshoot of FAS and CCE activities in a dose-dependent manner. In contrast, activities of Me, G6PDH and PGDH responded to low dietary lindane concentrations with a substantial stimulation of the increase of activity, whereas at high lindane concentrations the overshoot was inhibited. According to their responses to lindane exposure, liver lipogenic enzymes could be grouped into 2 categories with FAS and CCE representing one and ME, G6PDH and PGDH representing the other group. Polychlorinated biphenyls (PCBs) in the diet caused basically opposite changes of the activities of the lipogenic enzymes. Co-administration of lindane and PCBs resulted in an apparent cancellation of effects, suggesting that lindane and PCBs affect fatty acid synthesis at opposite points.(ABSTRACT TRUNCATED AT 250 WORDS)

The evolution of crassulacean acid metabolism inAeonium inferred from carbon isotope composition and enzyme activities.

Variation in crassulacean acid metabolism (CAM) was investigated in thirtyAeonium species under controlled, well-watered conditions. Carbon isotope ratios and the specific activities of the CAM enzymes phosphoenolpyruvate carboxylase (PEPC) and malic enzyme ME_ are highly correlated and indicate a large variation in CAM. The δ13C values range from -13.6 to -27.1‰; PEPC and ME activities vary seven- and five-fold, respectively. Since these observations were made under controlled conditions, the differences are genetically determined and represent adaptations to different habitats. The CAM activity of the species is correlated with the characteristics of their natural habitats. CAM activity is also highly correlated with the growth- and life-forms of the species and accordingly agrees well with the infrageneric classifications which are partly based on these characters. Our results support the hypothesis that the Sempervivoideae have evolved from an EurasiaticSedum, which used C3 photosynthesis or weak CAM, and that evolution withinAeonium was from undifferentiatedSedum-like dwarf shrubs with C3 photosynthesis to woody candelabrum-shaped shrubs exhibiting strong CAM. The monocarpic, rosulate species with intermediate CAM may have evolved via an independent secondary route.

Purification of NADP-malic Enzyme from Apple Fruit and its Change with Development and Ripening.

The molecular weight of NADP-malic enzyme (ME) in apple fruit is about 270, 000 and the enzyme molecule seems to be a tetramer composed of the same 4 subunits. The enzyme shows absolute specificity for NADP+ and no detectable activity when NAD+ replaced NADP+ in the assay mixture. The enzyme also requires a divalent cation such as Mn++ and Mg++ for its activity. In the presence of Mn++, optimum pH for the reaction was 7.5. The Km values for malate and NADP+ were 1.0 mM and 20.8 μM, respectivly. In the presence of Mg++, the Km values for malate and NADP+ at optimum pH of 7.2 were 4.0 mM and 60 μM, respectively.The ME activity increased with ripening, concomitant with an increase in the amount of enzyme protein determined by the ELISA method. The rate of increase in enzyme activity with ripening seems to be highest in late maturing apple cultivars.

Enzyme activity patterns of phosphoenolpyruvate carboxykinase, pyruvate kinase, glucose-6-phosphate-dehydrogenase and malic enzyme in human liver

The distribution patterns of the enzyme activities of phosphoenolpyruvate carboxykinase, pyruvate kinase, glucose-6-phosphate-dehydrogenase and malic enzyme were determined in the liver acini of men and women by microquantitative means. The activity of PEPCK was higher in men compared to the activity in women. In both sexes no heterotopic distribution pattern was observed. PK activity of men was higher, but in both sexes no heterotopic distribution was detectable. G6PDH and ME showed relatively low activity. The distribution of G6PDH and ME activity was to some extent different in men and women. Yet their heterotopic patterns were not particularly distinct.

Synthesis and oral activity of ME 1207, a new orally active cephalosporin.

Synthesis and oral activity of ME 1207, a new orally active cephalosporin.