Pyruvate Kinase Enzyme Activity Research Articles

Dynamics of and relationship between fat accumulation and enzyme activities of precocious walnut

Two precocious walnut varieties, Lvling and Lvzao were used as materials in this study, the kernel fat contents and 3 related enzyme activities in different development periods after flowe-ring 50 days were analyzed. The key enzymes affecting walnut fat in different periods were illumina-ted. The results showed that the kernel fat accumulation trends of the two varieties were basically the same. The kernel began to solidify 50 days after flowering, and the increase in kernel fat content was rapid 60-90 days after flowering, slowed down 90-120 days after flowering, and stopped 120-130 days after flowering. The Logistic model was used to fit the fat accumulation (P<0.01). Fat content rapid accumulation period was 57.8-85.8 days after flowering for Lvling, and 67.4-92.1 days after flowering for Lvzao. The activities of acetyl-CoA carboxylase (ACCase), 6-phosphate dextrose dehydrogenase (G6PDH) and pyruvate kinase (PK) increased from 50 to 100 days after flowering, and then the activities of enzymes began to decrease. The kernel fat content was positively correlated with the activity of ACCase. The kernel fat accumulation rate was positively correlated with PK enzyme activity. The correlation between fat content and enzyme activity was different at different development stages. The 50-100 days after flowering was the exuberant period of walnut kernel fat synthesis, and at this time the fat content could be improved by strengthening the field cultivation management measures. At the early stage of the walnut fat synthesis, G6PDH was the major enzyme to affect fat content, and PK activity influenced the formation of pyruvic acid, so as to indirectly affect the synthesis of fat. ACCase activity affected the final fat content and ACCase played an important regulating role in every period of fat synthesis. It was speculated that ACCase might be a key enzyme to affect the fat synthesis of walnut kernel.

Effect of infection by the protistan parasiteMarteilia refringenson the enzyme activity and energy reserves of oysterOstrea stentina(Payraudeau, 1826) in Tunisia

This is the first study of the metabolic enzyme activity and energy state of the dwarf oysterOstrea stentina(Payraudeau, 1826) in Tunisia and in the Mediterranean region. The main purpose of this study was to examine the modulation of the physiological status of the oysterO. stentinadepending on the season and the presence of parasiteMarteilia refringens. The prevalence of bonamiosis and marteiliosis were established by PCR.Bonamia exitiosawas detected only in 2.91% of oysters while the prevalence ofM. refringenswas 100% (30 Ind./30) in February and 93.93% (28 Ind./30) in March. A 42–87% mortality rate was reported during the study period. Biochemical analyses were carried out to evaluate the management of the energy resources in regard to the biochemical changes of lipids and carbohydrates. The enzyme activity of pyruvate kinase (PK), citrate synthase (CS) and cytochrome c oxidase (CCO) were measured and the mean level of enzyme activity was respectively 20.31 mU mg−1protein; 12.06 mU mg−1protein and 3.59 mU mg−1protein. Carbohydrate contents ofO. stentinawere very low all year round with an average of 15.18% in dry weight, and lipid contents remain similar (11.77% in dry weight) compared with the values reported for most other temperate bivalves. Enzyme activity significantly decreased over time (P&lt; 0.001). The energy resources of the oysterO. stentinawherein much of the energy was devoted to reproduction seem to affect the defence system.

Effect of HIV Infection and Antiretroviral Therapy on Some Red Cell Enzyme Activities and Coagulation Parameters

Aim: To assess G-6-PD, Pyruvate kinase enzyme activity and some coagulation parameters in HIV positive patients on antiretroviral treatment (ART) and those not on antiretroviral treatments with varying durations of infection and Antiretroviral treatments. Study Design: Case-control study Place and Duration of Study: Nnamdi Azikiwe University Teaching Hospital Nnewi, Nigeria from March to August 2013. Methodology: We included 181 subjects; Sixty HIV patients on ART with infection and ART duration of 5 – 8 and >8 – 17 years; Sixty HIV patients not on ART with an infection duration of 3 – 6 and >6 – 11 years; and Sixty-one apparently healthy individuals control. Glucose-6-Phosphate Dehydrogenase (G-6-PD) activity, Pyruvate kinase (PK) activity, Activated Partial Thromboplastin time (APTT), Prothrombin time

Abstract SY18-01: Alterations in metabolic pathways to support cancer cell proliferation

Abstract Unlike the majority of differentiated cells, many cancer cells metabolize glucose by aerobic glycolysis even in the presence of sufficient oxygen to support mitochondrial respiration. This phenomenon, also known as the Warburg effect, is characterized by increased glycolysis with lactate production and decreased oxidative phosphorylation. We have argued that aerobic glycolysis may be selected for by cancer cells to meet the distinct metabolic needs of proliferation. Unlike metabolism in differentiated cells, which is geared toward efficient ATP generation, the aerobic glycolysis observed in cancer cells appears to be adapted to facilitate the accumulation of biomass. Our understanding of how cancer cells meet their metabolic needs is based primarily on studies of cultured cells, and nutrient conditions in vitro differ significantly from those seen by tumor cells in vivo. Our long-term objective is to develop a comprehensive understanding on how cell metabolism is altered to accommodate anabolic synthesis and support the growth of tumors in vivo. The M2 isoform of pyruvate kinase (PK-M2) promotes the metabolism of glucose by aerobic glycolysis, contributes to anabolic metabolism, and appears necessary for optimal tumor growth in vivo. Paradoxically, these consequences of PK-M2 isoform selection are associated with decreased pyruvate kinase enzyme activity. Experiments to test the hypothesis that decreased pyruvate kinase activity promotes anabolic metabolism and cell proliferation in vivo will be presented. This includes data generated using genetically engineered mouse cancer models and small molecule activators of PK-M2. Additionally, efforts to understand pyruvate kinase-mediated regulation of glycolysis in cancer cells will be discussed. Decreased pyruvate kinase activity in cancer cells is accompanied by an alternate regulation of glycolysis. This creates a branch point in glycolysis to divert 3-phosphoglycerate into the serine biosynthesis pathway, and this reorganization of metabolic flux appears to be is important for proliferation. In fact, in some cancers a substantial portion of the total glucose flux is directed to serine synthesis and additional genetic evidence will be presented to suggest that glucose flux into this pathway can promote cell transformation. Finally, the role of the tumor environment, and how this contributes to the reorganization of metabolic pathways to support anabolic metabolism will be discussed. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr SY18-01. doi:10.1158/1538-7445.AM2011-SY18-01

Evidence for an alternative glycolytic pathway in rapidly proliferating cells.

Proliferating cells, including cancer cells, require altered metabolism to efficiently incorporate nutrients such as glucose into biomass. The M2 isoform of pyruvate kinase (PKM2) promotes the metabolism of glucose by aerobic glycolysis and contributes to anabolic metabolism. Paradoxically, decreased pyruvate kinase enzyme activity accompanies the expression of PKM2 in rapidly dividing cancer cells and tissues. We demonstrate that phosphoenolpyruvate (PEP), the substrate for pyruvate kinase in cells, can act as a phosphate donor in mammalian cells because PEP participates in the phosphorylation of the glycolytic enzyme phosphoglycerate mutase (PGAM1) in PKM2-expressing cells. We used mass spectrometry to show that the phosphate from PEP is transferred to the catalytic histidine (His11) on human PGAM1. This reaction occurred at physiological concentrations of PEP and produced pyruvate in the absence of PKM2 activity. The presence of histidine-phosphorylated PGAM1 correlated with the expression of PKM2 in cancer cell lines and tumor tissues. Thus, decreased pyruvate kinase activity in PKM2-expressing cells allows PEP-dependent histidine phosphorylation of PGAM1 and may provide an alternate glycolytic pathway that decouples adenosine triphosphate production from PEP-mediated phosphotransfer, allowing for the high rate of glycolysis to support the anabolic metabolism observed in many proliferating cells.

Insulinotropic effect of cinnamaldehyde on transcriptional regulation of pyruvate kinase, phosphoenolpyruvate carboxykinase, and GLUT4 translocation in experimental diabetic rats

Diabetes mellitus is a chronic metabolic disorder affecting about 6% of population worldwide with its complications and is rapidly reaching epidemic scale. Cinnamomum zeylanicum is widely used in alternative system of medicine for treatment of diabetes. In the present study, we have performed bioassay guided fractionation of chloroform extract of C. zeylaniucm and identified cinnamaldehyde (CND) as an active principle against diabetes. In continuation to it, a detailed study was undertaken to elucidate its mode of antidiabetic action in STZ induced diabetic rats. Oral administration of CND (20 mg/kg bw) to diabetic rats for 2 months showed significant improvement ( p < 0.001) in muscle and hepatic glycogen content. In vitro incubation of pancreatic islets with CND enhanced the insulin release compared to glibenclamide. The insulinotropic effect of CND was found to increase the glucose uptake through glucose transporter (GLUT4) translocation in peripheral tissues. The treatment also showed a significant improvement in altered enzyme activities of pyruvate kinase (PK) and phosphoenolpyruvate carboxykinase (PEPCK) and their mRNA expression levels. Furthermore, the median lethal dose (LD 50) of CND could not be obtained even at 20 times (0.4 g/kg bw) of its effective dose. With the high margin of safety of CND, it can be developed as a potential therapeutic candidate for the treatment of diabetes.

Transcriptional regulation of pyruvate kinase and phosphoenolpyruvate carboxykinase in the adductor muscle of the oyster Crassostrea gigas during prolonged hypoxia

The response of Crassostrea gigas to prolonged hypoxia was investigated for the first time by analyzing the metabolic branch point formed by pyruvate kinase (PK) and hosphoenolpyruvate carboxykinase (PEPCK). PK and PEPCK cDNAs were cloned and sequenced. The main functional domains of the PK sequence, such as the binding sites for ADP/ATP and phosphoenolpyruvate (PEP), were identified whereas the PEPCK sequence showed the specific domain to bind PEP in addition to the kinase-1 and kinase-2 motifs to bind guanosine triphosphate (GTP) and Mg(2+), specific for all PEPCKs. A C-terminal extension was detected for the first time in eukaryota PK. Separation of mitochondrial and cytosolic fraction showed that more than 92% of the PEPCK enzyme activity was cytosolic in gills, digestive gland, mantle and muscle. PK and PEPCK mRNAs and enzyme activities have been measured in muscle during prolonged hypoxia for 20 days. Adaptation of PK in hypoxic muscle at transcriptional level occurred lately by decreasing significantly the PK mRNA level at day 20 while PK enzyme activity was inhibited by the high content of alanine. The PEPCK mRNA ratio in hypoxic muscle significantly increased at day 10 simultaneously to the PEPCK enzyme activity. Succinate accumulation observed at day 10 and day 20 confirmed the anaerobic pathway of muscle metabolism in oyster subjected to hypoxia. Regulation of C. gigas PEPCK in muscle occurred at gene transcription level while PK was first regulated at enzyme level with alanine as allosteric inhibitor, and then at molecular level under a fast effect of hypoxia.

Kupffer cell cytokines interleukin-1$beta; and interleukin-10 combine to inhibit phosphoenolpyruvate carboxykinase and gluconeogenesis in cultured hepatocytes

Background and aims: Recent evidence suggests that inflammatory cytokines may mediate reduced hepatic glucose production and reduced blood glucose concentrations in sepsis. Therefore the aim of this study is to provide direct evidence of a cytokine-mediated interaction between Kupffer cells and hepatocytes by characterising the effects of lipopolysaccharide-stimulated Kupffer cells on hepatocyte gluconeogenesis, and the activity of key regulatory enzymes of this pathway. Methods and results: Primary isolates of hepatocytes co-cultured with lipopolysaccharide-stimulated Kupffer cells in Transwell inserts showed a 48% inhibition of gluconeogenesis (P<0.001). RNase protection assay and ELISA of Kupffer cells and the culture media following exposure to lipopolysaccharide showed increased levels of interleukin-1 alpha and beta, tumour necrosis factor alpha and IL-10. The addition of IL-1β and IL-10 to hepatocyte cultures inhibited gluconeogenesis by 52% (P<0.001), whereas each cytokine alone was ineffective. To determine whether altered production or activity of phosphoenolpyruvate carboxykinase or pyruvate kinase was responsible for the reduced glucose synthesis, their mRNA, protein levels and enzyme activities were measured. Primary hepatocytes co-cultured with lipopolysaccharide-stimulated Kupffer cells or cultured with a combination of IL-1β and IL-10 displayed reduced levels of phosphoenolpyruvate carboxykinase mRNA, protein and enzyme activity. In contrast the mRNA, protein levels and enzyme activity of pyruvate kinase were not altered; suggesting that gluconeogenesis was suppressed by downregulation of phosphoenolpyruvate carboxykinase. Conclusions: Therefore, hypoglycaemia, which is often observed in sepsis, may be mediated by Kupffer cell-derived IL-1β and IL-10. In addition this study suggests these cytokines inhibit phosphoenolpyruvate carboxykinase production and thereby hepatic gluconeogenesis.

Kupffer cell cytokines interleukin-1β and interleukin-10 combine to inhibit phosphoenolpyruvate carboxykinase and gluconeogenesis in cultured hepatocytes

Background and aims: Recent evidence suggests that inflammatory cytokines may mediate reduced hepatic glucose production and reduced blood glucose concentrations in sepsis. Therefore the aim of this study is to provide direct evidence of a cytokine-mediated interaction between Kupffer cells and hepatocytes by characterising the effects of lipopolysaccharide-stimulated Kupffer cells on hepatocyte gluconeogenesis, and the activity of key regulatory enzymes of this pathway. Methods and results: Primary isolates of hepatocytes co-cultured with lipopolysaccharide-stimulated Kupffer cells in Transwell inserts showed a 48% inhibition of gluconeogenesis ( P<0.001). RNase protection assay and ELISA of Kupffer cells and the culture media following exposure to lipopolysaccharide showed increased levels of interleukin-1 alpha and beta, tumour necrosis factor alpha and IL-10. The addition of IL-1β and IL-10 to hepatocyte cultures inhibited gluconeogenesis by 52% ( P<0.001), whereas each cytokine alone was ineffective. To determine whether altered production or activity of phosphoenolpyruvate carboxykinase or pyruvate kinase was responsible for the reduced glucose synthesis, their mRNA, protein levels and enzyme activities were measured. Primary hepatocytes co-cultured with lipopolysaccharide-stimulated Kupffer cells or cultured with a combination of IL-1β and IL-10 displayed reduced levels of phosphoenolpyruvate carboxykinase mRNA, protein and enzyme activity. In contrast the mRNA, protein levels and enzyme activity of pyruvate kinase were not altered; suggesting that gluconeogenesis was suppressed by downregulation of phosphoenolpyruvate carboxykinase. Conclusions: Therefore, hypoglycaemia, which is often observed in sepsis, may be mediated by Kupffer cell-derived IL-1β and IL-10. In addition this study suggests these cytokines inhibit phosphoenolpyruvate carboxykinase production and thereby hepatic gluconeogenesis.

The effect of benzene on serum hormones and the activity of some enzymes in different tissues of rats

The effects of a 100 mg.kg -1 dose of benzene, an occupational and environmental toxicant, were investigated on serum, estradiol and testosterone concentrations as well as lactate dehydrogenase (LDH), alkaline phosphatase (ALP), alanine amino transferase (ALT), aspartate amino transferase (AST), and pyruvate kinase (PK) activities in the liver and kidney of rats after 2, 4, 8, 16, 32, 64 and 72 hours. Benzene was given intraperitoneally to Rat rattus norvegicus and the control groups were injected with physiological saline. Liver tissue LDH, AST, ALT and kidney tissue LDH, ALP, AST, ALT activities were lower in the benzene treated group when compared to those in the control group (p<0.05). A tendency for an increase in the liver tissue ALP activity was observed, which was significant at 8 and 16 hours (p<0.05). There were significant increases in ALT in the liver and LDH, AST, and ALT enzyme activities in the kidney tissue at the beginning of the experiment in both groups and these activities were found to be nearly the same. Pyruvate kinase enzyme activities in rats given benzene were slightly increased in kidney tissues but lower in liver tissues. Differences between the groups tended to disappear towards the end of the experimental period. However, serum estradiol concentrations in the serum diverged significantly (p<0.05). Consequently, it was found that benzene administration led to some changes (increases then decreases) in LDH, ALP, ALT, AST, and PK activity and estradiol, testosterone concentrations in different tissues of rats. Possible causes of the increases and decreases in enzyme activities and hormone levels are discussed.

Dietary polyunsaturated fatty acids interfere with the insulin/glucose activation of L-type pyruvate kinase gene transcription.

L-type pyruvate kinase (L-PK) is a key glycolytic enzyme regulating the flux of metabolites through the pyruvate-phosphoenolpyruvate cycle (1). The regulation of L-PK is complex involving both hormones and nutrients. We have found that feeding rats diets containing polyunsaturated fatty acids (PUFA) significantly inhibits hepatic pyruvate kinase enzyme activity (> 60%) and suppresses mRNAPK abundance (> 70%). Studies with primary hepatocytes indicate that PUFA act directly on hepatocytes. Specifically, arachidonic (20:4, omega 6) and eicosapentaenoic (20:5, omega 3) acid suppressed both mRNAPK llevels and the activity of a transfected PKCAT (-4300/+12) fusion gene by > 70%. This is due to an inhibition of the insulin/glucose-mediated transactivation of L-PKCAT. Deletion analysis localized PUFA-regulated cis-acting elements to a region within the L-PK proximal promoter, i.e. between -197 and -96 base pairs. This region binds two transcription factors involved in the hormone/nutrient regulation of L-PK gene transcription, i.e. a major late transcription factor-like factor and HNF-4. Linker scanning mutation analysis localized the PUFA-regulated cis-acting elements to the vicinity of the HNF-4 binding site. Thus, PUFA-regulated factors abrogate the insulin/glucose activation of L-PK gene transcription by targeting the HNF-4 elements. These studies suggest that PUFA may have significant effects on hepatic carbohydrate metabolism by inhibiting the L-PK side of the pyruvate-phosphoenolpyruvate cycle.

Substrate cycling between pyruvate and oxaloacetate in awake normal and 3,3'-5-triiodo-L-thyronine-treated rats.

Substrate cycling between pyruvate and oxaloacetate was assessed in awake 24-h fasted normal and triiodothyronine (T3)-treated rats. After a 20- or 60-min infusion of [3-13C]alanine (99% enriched, 12 mg/min) the 13C enrichments of liver glucose and alanine carbons were analyzed by 13C and 1H nuclear magnetic resonance spectroscopy and gas chromatography-mass spectrometry. Substrate cycling from phosphoenolpyruvate to pyruvate [via pyruvate kinase (PK)] and from oxaloacetate to pyruvate [via malic enzyme (ME)] relative to the pyruvate carboxylase (PC) flux [i.e., (PK+ME)/PC] was assessed by the ratio of the 13C enrichment of C-2 alanine relative to that in C-5 glucose. In the normal rats (PK+ME)/PC was 0.26 +/- 0.07 (n = 7, t = 20 min) and 0.37 +/- 0.08 (n = 4, t = 60 min). In the T3-treated rats the (PK+ME)/PC increased four- to fivefold to 1.03 +/- 0.19 (n = 8, t = 20 min) and to 1.83 +/- 0.19 (n = 3, t = 60 min) (P < 0.05 vs. normal rats). The liver enzyme activity of PK did not change with T3 treatment (normal 14.22 +/- 5.25 U/g liver vs. T3 treated 13.40 +/- 1.10 U/g liver), whereas both the enzyme activity ratio of PK (normal 0.47 +/- 0.15 vs. T3 treated 0.77 +/- 0.03, P < 0.05) and the activity of ME (normal 0.89 +/- 0.30 U/g liver vs. T3 treated 4.25 +/- 0.60 U/g liver, P < 0.05) increased with T3 treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of chronic renal failure on the regulation of pyruvate kinase

The effects of chronic renal failure on the enzyme activity of pyruvate kinase and the mRNA level of this enzyme were studied in 7 out of 8 nephrectomized rats. The mRNA level was measured by RNA-DNA dot blot hybridization, using cloned pyruvate kinase cDNA as hybridized probe. Neither the activity of M 1-type pyruvate kinase nor the level of this enzyme in rat gastrocnemius muscle was affected by chronic renal failure, whereas l-type pyruvate kinase enzyme activity in uremic rat liver was lower than that in control at both fasted and refed states. The levels of l-type pyruvate kinase mRNA were not different between two groups as the fasted state. Induction of l-type pyruvate kinase mRNA after high carbohydrate diet refeeding was suppressed proportionally to the severity of chronic renal failure, which was expressed by the serum creatine concentrations ( r = −.876, P < .005). These results indicate that the suppression of l-type pyruvate kinase activity in uremia was partly reflected by the decreased accumulation of this enzyme mRNA. There was a significantly negative correlation between l-type pyruvate kinase mRNA levels and plasma glucagon/insulin ratios ( r = −.719, P < .05). Hyperglucagonemia in uremia might play a major role in this suppression.

Frequency of erythrocyte pyruvate kinase deficiency in Chinese infants.

The incidence of deficiency of the enzyme pyruvate kinase (PK) in Chinese infants was determined. Both the standard assay of erythrocyte pyruvate kinase enzyme activity and a fluorescent screening test (standardized) were used. The results of these two tests were compared. Of 1,159 infant cord blood samples studied, 26 (or 2.2%) had abnormally low levels of PK activity using the screening test, as did 24 of the samples tested by the enzyme assay. The results indicate that the frequency of a defective PK gene in the population of Guangzhou is significantly lower (p less than .05) than the previously reported defective gene frequency of 3.4% in Hong Kong. They also demonstrate the critical importance of standardization of the screening test, if most accurate estimates of gene frequency are to be derived by using this test.

The isolation, characterization, and sequence of the pyruvate kinase gene of Saccharomyces cerevisiae.

The Saccharomyces cerevisiae gene encoding the glycolytic enzyme pyruvate kinase has been isolated by complementation of a pyk mutant with DNA from a wild type yeast genomic library. Pyruvate kinase enzyme activity is 20-fold higher in the transformant compared to the parental strain and is glucose inducible. The cloned gene has been localized by hybridization of DNA fragments to yeast poly(A+) RNA and by complementation of the mutant defect with select subclones. A DNA sequence of 2885 nucleotides encoding a protein of 499 amino acids is reported. A polypeptide chain of 34 residues of the deduced yeast amino acid sequence closely resembles a peptide sequence at the ADP binding site of bovine muscle pyruvate kinase. The 5' end of the pyruvate kinase mRNA has been mapped and starts within the DNA sequence CAAG at -38 to -27 nucleotides upstream from the first ATG. We note that the sequence PyAAPu in this region appears to be a common consensus site for yeast RNA polymerase II transcriptional starts.

Immunologic study of the age-related loss of activity of six enzymes in the red cells from newborn infants and adults--evidence for a fetal type of erythrocyte phosphofructokinase.

Blood from 10 normal healthy adults and cord blood from 8 healthy full term infants were infiltrated through a mixture sulfoethylethycellulose-Sephadex G 25 in order to eliminate the platelets and the leukocytes. Then the erythrocytes were fractionated into young and old cells by centrifugation in microhematocrit tubes. The enzyme activity and the immunologic reactivity of glucose phosphate isomerase (EC.5.3.1.9), phosphoglycerate kinase (EC.2.7.2.3), pyruvate kinase (ec.2.7.1.40), glucose 6-phosphate dehydrogenase (EC. 1.1.1.49), and 6-phosphogluconate dehydrogenase (EC.1.1.1.44) were measured in every fraction. As previously reported, the enzyme activities were far higher in cord blood than in adult blood red cells; nevertheless, the age-related loss of enzyme activity was similar in both cord and adult blood. The decrease of the enzyme activity of glucose phosphate isomerase and phosphoglycerate kinase in old cells was singly associated with a lowered concentration of the enzyme-related antigen; by contrast, the age-related decrease of the enzyme activity of pyruvate kinase, glucose-6-phosphate dehydrogenase, and 6-phosphogluconate dehydrogenase was associated with both a lowered concentration of the enzyme-related antigen and a lowered "molecular specific activity" (i.e., a lowered ratio of enzyme activity to enzyme-related antigen concentration). This phenomenon was especially marked for pyruvate kinase, which had a molecular specific activity in old cells that was 68% of that in young cells. Phosphofructokinase had a lower enzyme activity in cord blood erythrocytes than in adult blood erythrocytes; the difference was especially important in old cells from infants in which phosphofructokinase activity was 53% of that in old cells from adults. Phosphofructokinase from old cells of full term infants and from unfractionated cells from two premature infants (21 and 32 weeks of gestation) was less neutralized by anti-muscle phosphofructokinase serum and more inhibited by ATP than the enzyme from adult blood erythrocytes.

Effects of Quantity and Quality of Dietary Protein and Variation in Certain Enzyme Activities on Glucose Metabolism in the Rat

This study attempted to determine whether the quantity and the quality of protein intake could influence the activity of some enzymes involved in carbohydrate metabolism. Thus, adult rats were fed for 23 days a diet containing different levels (10 to 70%) and qualities (casein, wheat gluten, and egg yolk) of protein. Variations in liver enzyme activities of pyruvate kinase (PK), glucose-6-phosphate dehydrogenase (G6PDH), malic enzyme (ME), glucose-6-phosphatase (G6Pase), and phosphoenolpyruvate carboxykinase (PEPCK) were studied. Also the changes in enzyme activities were compared with changes in food intake and body weight gain. Increasing the protein level produced a progressive fall in the activities of ME and PK. The decrease in PK activity was greater when the biological value of the dietary proteins was higher (P less than 0.05). On the other hand, the activities of G6PDH and PEPCK increased as the protein level increased. The activity of G6Pase was unchanged. The relationship between the two opposing enzyme activities PK and PEPCK, in relation to protein intake, shows that for each protein studied, the equilibrium between glycolysis and gluconeogenesis was obtained at different protein intakes (1.5, 1.9, and 2.2 g of protein/day/100 g of body weight, respectively, for egg yolk, casein, and wheat gluten) regardless of daily consumption of energy as carbohydrate, which are similar (8 to 9 kcal/day/100 g of body weight). This equilibrium also corresponded to the maximum weight gain (5 g) of the experimental animals. In conclusion, the experimental method used permits a simultaneous assessment of the protein and carbohydrate requirements ensuring the best weight gain in young adult rats.

Differentiation of liver metabolism on the molecular level during chronic application of halothane

Mice were treated with Halothane (0.5 % in O 2) 1 hr daily for 4 weeks. During this period, enzyme activities and substrate contents were measured in the liver and compared with the livers of untreated mice. During Halothane treatment, the relative liver weight increased rapidly (30–50 per cent in the first week) while protein and glycogen content of the liver and the general enzyme pattern remained constant (related per g liver wt.); that means that a coordinate growth occurs. Only few enzymes changed in their activity; there was a decrease in the enzyme activity of pyruvate kinase and an increase of malic enzyme and glycerol-1-phosphate oxidase activity. The substrate content in the trioses of the Embden Meyerhof chain was diminished, whereas substrates of the citric acid cycle were increased. The effects observed are discussed with respect to the observations made by other authors and compared with the effects after barbiturate treatment.