Showing papers on "Pyruvate kinase published in 1978"

Pathway of succinate and propionate formation in Bacteroides fragilis.

Abstract: Cell suspensions of Bacteroides fragilis were allowed to ferment glucose and lactate labeled with 14C in different positions. The fermentation products, propionate and acetate, were isolated, and the distribution of radioactivity was determined. An analysis of key enzymes of possible pathways was also made. The results of the labeling experiments showed that: (i) B. fragilis ferments glucose via the Embden-Meyerhof pathway; and (ii) there was a randomization of carbons 1, 2, and 6 of glucose during conversion to propionate, which is in accordance with propionate formation via fumarate and succinate. The enzymes 6-phosphofrucktokinase (pyrophosphate-dependent), fructose-1,6-diphosphate aldolase, phosphoenolpyruvate carboxykinase, malate dehydrogenase, fumarate reductase, and methylmalonyl-coenzyme A mutase could be demonstrated in cell extracts. Their presence supported the labeling results and suggested that propionate is formed from succinate via succinyl-, methylmalonyl-, and propionyl-coenzyme A. From the results it also is clear that CO2 is necessary for growth because it is needed for the formation of C4 acids. There was also a randomization of carbons 1, 2, and 6 of glucose during conversion to acetate, which indicated that pyruvate kinase played a minor role in pyruvate formation from phosphoenolpyruvate. Phosphoenolpyruvate carboxykinase, oxaloacetate decarboxylase, and malic enzyme (nicotinamide adenine dinucleotide phosphate-dependent) were present in cell extracts of B. fragilis, and the results of the labeling experiments agreed with pyruvate synthesis via oxaloacetate and malate if these acids are in equilibrium with fumarate. The conversion of [2-14C]- and [3-14C]lactate to acetate was not associated with a randomization of radioactivity.

Glycolysis mutants in Saccharomyces cerevisiae.

Abstract: Mutants have been isolated in S. cerevisiae with the phenotype of growth on pyruvate but not on glucose, or growth on rich medium with pyruvate but inhibition by glucose. Screening of mutagenized cultures was either without an enrichment step, or after enrichment using the antibiotic netropsin (Young et al. 1976) or inositol starvation ( Henry, Donahue and Culbertson 1975). One class of mutants lacked pyruvate kinase (pyk), another class had all the enzymes of glycolysis, and one mutant lacked phosphoglucose isomerase (pgi, Maitra 1971). Partial reversion of pyruvate kinase mutants on rich medium containing glucose gave double mutants now also lacking hexokinase (hxk ), phosphofructokinase (pfk), or several enzymes of glycolysis (gcr). In diploids the mutations were recessive. pyk, pgi, pfk , and gcr segregated 2:2 from their wild-type alleles. PYK hxk, PYK pfk, and PYK gcr segregants grew on glucose.

Hemolytic anemia in disorders of red cell metabolism

Abstract: 1 The Red Cell.- 1.1. Red Cell Structure.- 1.2. Red Cell Metabolism.- 1.2.1. Embden-Meyerhoff Pathway.- 1.2.2. Hexose Monophosphate Pathway.- 1.2.3. Other Pathways.- 1.2.4. ATPase Activity and Ion Movements.- 1.2.5. Methemoglobin Reduction.- References.- 2 Glucose-6-Phosphate Dehydrogenase Deficiency.- 2.1. History.- 2.2. Genetics and Population Distribution.- 2.3. Glucose-6-phosphate Dehydrogenase.- 2.3.1. Purification.- 2.3.2. Subunit Structure.- 2.3.3. Kinetic Properties.- 2.3.4. Biochemical Properties of Variants.- 2.4. Physiology and Pathophysiology.- 2.4.1. The Steady State.- 2.4.1.1. Red Cells.- 2.4.1.2. White Cells.- 2.4.1.3. Platelets.- 2.4.1.4. Other Tissues.- 2.4.2. Association of Various Disease States with G-6-PD Deficiency.- 2.4.2.1. Nonhematologic Changes.- 2.4.2.2. Drug-Induced Hemolytic Anemia.- 2.4.2.3. Hemolytic Anemia Induced by Infection.- 2.4.2.4. Hemolytic Anemia in Diabetic Acidosis.- 2.4.2.5. Neonatal Icterus.- 2.4.2.6. Favism.- 2.4.2.6a. The Predisposition to Favism.- 2.4.2.6b. The Active Factor.- 2.4.2.7. Hereditary Nonspherocytic Hemolytic Anemia.- 2.5. Diagnosis.- 2.6. Treatment.- References.- 3 Pyruvate Kinase Deficiency.- 3.1. History.- 3.2. Genetics.- 3.3. Acquired Pyruvate Kinase Deficiency.- 3.4. Pyruvate Kinase.- 3.4.1. The Normal Enzyme.- 3.4.2. Mutant Pyruvate Kinase.- 3.5. The Pyruvate Kinase-Deficient Red Cell.- 3.6. Clinical Manifestations.- 3.7. Diagnosis.- 3.8. Treatment.- References.- 4 Hemolytic Anemia Due to Other Enzyme Deficiencies.- 4.1. Hexokinase Deficiency.- 4.2. Glucose Phosphate Isomerase Deficiency.- 4.3. Phosphofructokinase Deficiency.- 4.4. Aldolase Deficiency.- 4.5. Triose Phosphate Isomerase Deficiency.- 4.6. Phosphoglycerate Kinase Deficiency.- 4.7. Glyceraldehyde Phosphate Dehydrogenase Deficiency.- 4.8. Diphosphoglycerate Mutase Deficiency.- 4.9. Diphosphoglycerate Phosphatase Deficiency.- 4.10. Enolase Deficiency.- 4.11. Defects in Glutathione Synthesis.- 4.12. Glutathione Reductase Deficiency.- 4.13. Glutathione Peroxidase Deficiency.- 4.14. Phosphogluconate Dehydrogenase Deficiency.- 4.15. Disorders of Nucleotide Metabolism.- 4.15.1. ATPase Deficiency.- 4.15.2. Adenylate Kinase Deficiency.- 4.15.3. "High ATP" Syndromes.- 4.15.4. Pyrimidine 5?-Nucleotidase Deficiency.- 4.15.5. Increased Adenosine Deaminase Activity.- References.

The regulation of liver pyruvate kinase by phosphorylation--dephosphorylation.

Abstract: Publisher Summary This chapter discusses the regulation of liver pyruvate kinase by phosphorylation–dephosphorylation. The rate and extent of the phosphorylation of L-type liver pyruvate kinase in vitro indicate that it is a specific reaction. This is supported by inhibition of the enzyme by the phosphorylation, which may be expected with regard to the known effect of cAMP on liver gluconeogenesis. The specificity of the phosphorylation reaction is also demonstrated by the fact that neither the A-type enzyme from pig kidney nor the M-type muscle enzyme from the rabbit or pig are substrates of cAMP-stimulated protein kinase. However, phosphorylation of the type-A enzyme from chicken liver has been preliminarily reported. The phosphorylation of liver pyruvate kinase in vitro is reversible, owing to the presence in rat liver cell sap of phosphoprotein phosphatase, which acts on phosphorylated pyruvate kinase. In vitro experiments strongly indicate that L-type liver pyruvate kinase is an enzyme whose activity is regulated by reversible protein phosphorylation in vivo .

Growth state-dependent phenotypes of adult hepatocytes in primary monolayer culture.

Abstract: A proliferation-competent adult rat liver cell monolayer system has been analyzed for tissue-specific functions during its growth cycle. High levels of the adult (L type) form of pyruvate kinase (EC 2.7.1.40) and glutathione S-transferase B ("ligand," EC 2.5.1.18) are observed during the early lag phase; they decline markedly during the logarithmic phase and reappear during the stationary phase. By contrast, elevated levels of the fetal (K type) form of pyruvate kinase and alpha1-fetoprotein production appear only after proliferation begins; this pattern diminishes slightly during stationary phase as the adult phenotype is restored. Albumin production continues throughout the entire growth cycle. These in vitro findings simulate those observed during hepatoproliferative transitions in the intact animal and, as such, constitute a developmental program for normal epithelial cells in primary culture.

In vivo regulation of glycolysis and characterization of sugar: phosphotransferase systems in Streptococcus lactis.

Abstract: Two novel procedures have been used to regulate, in vivo, the formation of phosphoenolpyruvate (PEP) from glycolysis in Streptococcus lactis ML3. In the first procedure, glucose metabolism was specifically inhibited by p-chloromercuribenzoate. Autoradiographic and enzymatic analyses showed that the cells contained glucose 6-phosphate, fructose 6-phosphate, fructose-1,6-diphosphate, and triose phosphates.Dithiothreitol reversed the p-chloromercuribenzoate inhibition, and these intermediates were rapidly and quantitatively transformed into 3- and 2-phosphoglycerates plus PEP. The three intermediates were not further metabolized and constituted the intracellular PEP potential. The second procedure simply involved starvation of the organisms. The starved cells were devoid of glucose 6-phosphate, fructose 6-phosphate, fructose- 1,6-diphosphate, and triose phosphates but contained high levels of 3- and 2-phosphoglycerates and PEP (ca. 40 mM in total). The capacity to regulate PEP formation in vivo permitted the characterization of glucose and lactose phosphotransferase systems in physiologically intact cells. Evidence has been obtained for "feed forward" activation of pyruvate kinase in vivo by phosphorylated intermediates formed before the glyceraldehyde-3-phosphate dehydrogenase reaction in the glycolytic sequence. The data suggest that pyruvate kinase (an allosteric enzyme) plays a key role in the regulation of glycolysis and phosphotransferase system functions in S. lactis ML3.

Guanylate kinases from human erythrocytes, hog brain, and rat liver.

Abstract: Publisher Summary This chapter describes the purification procedure of guanylate kinases from human erythrocytes, hog brain, and rat liver. A convenient assay involves the measurement of both adenosine diphosphate (ADP) and guanosine diphosphate (GDP) formed from adenosine triphosphate (ATP) and guanosine monophosphate (GMP) to pyruvate kinase and lactate dehydrogenase reactions. The decrease in absorbancy at 340 nm associated with NADH oxidation is measured with a spectrophotometer using a blue filter. All procedures steps are performed at 0–4°. Enzymic activities and protein concentrations are determined after each step of purification. The purified guanylate kinases from the sources that are given in the chapter, were found stable for several years when stored below 0° in the presence of 70% saturated ammonium sulfate. In experiments with partially purified erythrocytic guanylate kinase, significant activity was retained for several minutes after precipitation at 3% perchloric acid followed by neutralization with potassium hydroxide.

Control of gluconeogenesis and of enzymes of glycogen metabolism in isolated rat hepatocytes. A parallel study of the effect of phenylephrine and of glucagon.

Abstract: Hepatocytes isolated from the livers of fed rats were used for a comparative study of the effects of phenylephrine, vasopressin and glucagon on gluconeogenesis and on enzymes of glycogen metabolism. When hepatocytes were incubated in the presence of Ca(2+), phenylephrine stimulated gluconeogenesis from pyruvate less than did glucagon, but, in contrast with this hormone, it did not affect the activities of protein kinase and pyruvate kinase, nor the concentration of phosphoenolpyruvate, and it did not decrease the release of (3)H(2)O from [6-(3)H]glucose. The effects of vasopressin were similar to those of phenylephrine. Gluconeogenesis from fructose was also stimulated by phenylephrine and, more markedly, by glucagon at the expense of the conversion of fructose into lactate. Insulin was able to antagonize the stimulatory effect of phenylephrine on gluconeogenesis from pyruvate. When Ca(2+) was removed from the incubation medium, phenylephrine still stimulated gluconeogenesis from pyruvate, but it also caused an activation of protein kinase and an inactivation of pyruvate kinase; accordingly, the concentration of phosphoenolpyruvate was increased, and, in contrast, vasopressin had no effect on all these parameters. The property of phenylephrine to cause the activation of glycogen phosphorylase was decreased by glucose or by the absence of Ca(2+); it was abolished when these two conditions were combined. Glycogen synthase was inactivated by phenylephrine in the presence or the absence of Ca(2+), although presumably by different mechanisms.

Maximum activities and effects of fructose bisphosphate on pyruvate kinase from muscles of vertebrates and invertebrates in relation to the control of glycolysis.

Abstract: 1. Comparison of the maximum activities of pyruvate kinase with those of phosphofructokinase in a large number of muscles from invertebrates and vertebrates indicates that, in general, in any individual muscle, the activity of pyruvate kinase is only severalfold higher than that of phosphofructokinase. This is consistent with the suggestion, based on mass-action ratio data, that the pyruvate kinase reaction is non-equilibrium in muscle. However, the range of activities of pyruvate kinase in these muscles is considerably larger than that of phosphofructokinase. This difference almost disappears if the enzyme activities from muscles that are known to possess an anaerobic ;succinate pathway' are excluded. It is suggested that, in these muscles, phosphofructokinase provides glycolytic residues for both pyruvate kinase (i.e. glycolysis) and phosphoenolpyruvate carboxykinase (i.e. the succinate pathway). This is supported by a negative correlation between the activity ratio, pyruvate kinase/phosphofructokinase, and the activities of nucleoside diphosphokinase in these muscles, since high activities of nucleoside diphosphokinase are considered to indicate the presence of the succinate pathway. 2. The effect of fructose bisphosphate on the activities of pyruvate kinase from many different muscles was studied. The stimulatory effect of fructose bisphosphate appears to be lost whenever an efficient system for supply of oxygen to the muscles is developed (e.g. insects, squids, birds and mammals). This suggests that activation of pyruvate kinase is important in the co-ordinated regulation of glycolysis in anaerobic or hypoxic conditions, when the change in glycolytic flux during the transition from rest to activity needs to be large in order to provide sufficient energy for the contractile activity. However, lack of this effect in the anaerobic muscles of the birds and mammals suggests that another metabolic control may exist for avian and mammalian pyruvate kinase in these muscles.

Structure of pyruvate kinase and similarities with other enzymes: possible implications for protein taxonomy and evolution.

Abstract: The structure determination of pyruvate kinase shows that each subunit of the tetrameric molecule consists of three domains. The largest of these domains has a remarkable similarity to the structure of triosephosphate isomerase. Another domain shows similarities to many other nucleotide binding proteins. We discuss these similarities and their implications for current arguments on protein taxonomy and evolution.

Effects of Ammonia on Carbon Metabolism in Photosynthesizing Isolated Mesophyll Cells from Papaver somniferum L.

Abstract: Addition of ammonia to a suspension of photosynthesizing isolated mesophyll cells from P. somniferum quantitatively alters the pattern of carbon metabolism by increasing rates of certain key ratelimiting steps leading to amino-acid synthesis and by decreasing rates of rate-limiting steps in alternative biosynthetic pathways. Of particular importance is the stimulation of reactions mediated by pyruvate kinase and phosphoenolpyruvate carboxylase. The increased rates of these two reactions, which result in an increased flow of carbon into the tricarboxylic-acid cycle, correlate with a rapid rise in glutamine (via glutamine synthetase) which draws carbon off the tricarboxylic-acid cycle as α-ketoglutarate. Increased flux of carbon in this direction appears to come mainly at the expense of sucrose synthesis. The net effect of addition of ammonia to mesophyll cells is thus a redistribution of newly fixed carbon away from carbohydrates and into amino acids.

Energy metabolism in the mantle muscle of the squid,Loligo pealeii

Abstract: 1. The concentrations of glycolytic and Krebs cycle intermediates, α-glycerophosphate, the adenylates, and free amino acids were determined in the mantle muscle of the squid,Loligo pealeii, at rest and after 10 s of vigorous swimming. 2. Exercise resulted in significant increases in the levels of glucose-6-phosphate, fructose-1,6-diphosphate, and pyruvate. Phosphofructokinase and pyruvate kinase were identified as control points of glycolysis. In the Krebs cycle, changes in the levels of isocitrate and α-ketoglutarate suggested a facilitation of the isocitrate dehydrogenase reaction. 3. The products of anaerobic metabolism in mantle muscle, in particular α-glycerophosphate and octopine, did not accumulate during exercise indicating the aerobic nature of “burst” swimming in these animals. 4. Exercise resulted in a drop in muscle proline concentrations of approximately 2 μmol/g wet wt. which was accompanied by an almost stoichiometric increase in alanine levels. 5. The changes in adenylate concentrations with exercise were dramatic: ATP fell to 39% of the value in resting muscle while ADP and AMP rose 3- and 6-fold, respectively. Arginine phosphate concentrations fell from 10 μmol/g wet wt. in resting to 1 μmol/g wet wt. in exercised muscle. 6. Muscular work in this squid appears to be accompanied by an activation of aerobic carbohydrate metabolism, the α-glycerophosphate cycle functioning to maintain cytoplasmic redox balance. During metabolic activation, the carbon skeleton of proline may be used to augment the pool size of Krebs cycle intermediates. The observed changes in arginine phosphate and AMP levels could be key in the activation of the reactions of glycolysis.

Properties of pyruvate kinase and phosphoenolpyruvate carboxykinase in relation to the direction and regulation of phosphoenolpyruvate metabolism in muscles of the frog and marine invertebrates

Abstract: 1. The properties of pyruvate kinase and, if present, phosphoenolpyruvate carboxykinase from the muscles of the sea anemone, scallop, oyster, crab, lobster and frog were investigated. 2. In general, the properties of pyruvate kinase from all muscles were similar, except for those of the enzyme from the oyster (adductor muscle); the pH optima were between 7.1 and 7.4, whereas that for oyster was 8.2; fructose bisphosphate lowered the optimum pH of the oyster enzyme from 8.2 to 7.1, but it had no effect on the enzymes from other muscles. Hill coefficients for the effect of the concentration of phosphoenolpyruvate were close to unity in the absence of added alanine for the enzymes from all muscles except oyster adductor muscle; it was 1.5 for this enzyme. Alanine inhibited the enzyme from all muscles except the frog; this inhibition was relieved by fructose bisphosphate. Low concentrations of alanine were very effective with the enzyme from the oyster (50% inhibition was observed at 0.4mm). Fructose bisphosphate activated the enzyme from all muscles, but extremely low concentrations were effective with the oyster enzyme (0.13μm produced 50% activation). 3. In general, the properties of phosphoenolpyruvate carboxykinase from the sea anemone and oyster muscles are similar: the Km values for phosphoenolpyruvate are low (0.10 and 0.13mm); the enzymes require Mn2+ in addition to Mg2+ for activity; and ITP inhibits the enzymes and the inhibition is relieved by alanine. These latter compounds had no effect on enzymes from other muscles. 4. It is suggested that changes in concentrations of fructose bisphosphate, alanine and ITP produce a coordinated mechanism of control of the activities of pyruvate kinase and phosphoenolpyruvate carboxykinase in the sea anemone and oyster muscles, which ensures that phosphoenolpyruvate is converted into oxaloacetate and then into succinate in these muscles under anaerobic conditions. 5. It is suggested that in the muscles of the crab, lobster and frog, phosphoenolpyruvate carboxykinase catalyses the conversion of oxaloacetate into phosphoenolpyruvate. This may be part of a pathway for the oxidation of some amino acids in these muscles.

Adenosine 5'-O-([gamma-18O]gamma-thio)triphosphate chiral at the gamma-phosphorus: stereochemical consequences of reactions catalyzed by pyruvate kinase, glycerol kinase, and hexokinase

Abstract: The 2-[18O]phosphorothioate of D-glycerate, chiral at phosphorus, was prepared. The chiral phosphoryl group was transferred enzymically to ADP [by using enolase and pyruvate kinase (ATP:pyruvate 2-O-phosphotransferase; EC 2.7.1.40)] resulting in the synthesis of adenosine 5'-O-([gamma-18O],gamma-thio)triphosphate. This labeled ATP was used as a thiophosphoryl group donor in the reactions catalyzed by glycerol kinase (ATP:glycerol 3-phosphotransferase; EC 2.7.1.30) and by hexokinase (ATP:D-hexose 6-phosphotransferase; EC 2.7.1.1). The product from the latter (glucose 6-phosphorothioate) was converted enzymically into glycerol phosphorothioate. Determination of the relative configurations and diastereoisomeric purities of the samples of glycerol phosphorothioate demonstrates that all three phosphokinases (pyruvate kinase, glycerol kinase, and hexokinase) transfer the thiophosphoryl group with complete stereospecificity, and further shows that these reactions follow an identical stereochemical course.

Isozymes of Pyruvate Kinase from Human Brain, Meningiomas, and Malignant Gliomas

Abstract: Pyruvate kinase isozymes were studied in normal brain tissue (both fetal and adult) and in meningiomas and malignant gliomas. In fetal brain five different forms could be detected by electrophoresis (K4, K3M, K2M2, KM3, and M4). In adult brain the M4-type, K3M hybrid, and K4-type are present; the M isozyme is largely predominant. Alanine inhibition of pyruvate kinase is in agreement with the electrophoretic pattern. Pyruvate kinase from fetal brain and brain of a newborn is more inhibited compared with pyruvate kinase from adult brain. The Lineweaver-Burk plots for pyruvate kinase from fetal brain and brain of the newborn are nonlinear due to the presence of hybrids. Pyruvate kinase from meningiomas and malignant gliomas is strongly inhibited by alanine. Electrophoresis proved the presence of mainly K4 type and the hybrid K3M, which is in agreement with the alanine inhibition. Determination of the Km's for phosphoenolpyruvate supports this conclusion. The determination of the alanine inhibition of pyruvate kinase may be a diagnostic tool in surgery for gliomas.

Properties of pyruvate kinase from soybean nodule cytosol.

Abstract: The properties of pyruvate kinase from soybean (Glycine max L.) nodule cytosol were examined to determine what influence the N2 fixation process might have on this supposed key control enzyme. A crude enzyme preparation was prepared by chromatography of cytosol extract on a diethylaminoethyl-cellulose column. ATP and citrate at 5 mm concentrations inhibited pyruvate kinase 27 and 34%, respectively. Enzyme activation was hyperbolic with respect to both K+ and NH4+ concentrations. In the presence of physiological concentrations of K+ and high phosphoenolpyruvate (PEP) concentrations, NH4+ inhibited enzyme activity. Comparisons of kinetic parameters (Vmax and apparent Ka) for NH4+ and K+ with inhibition curves indicated that inhibition was very likely a result of competition of the ions for activation site(s) on the pyruvate kinase. In addition, apparent Ka (monovalent cation) and Km (PEP) were influenced by PEP and monovalent cation concentrations, respectively. This effect may reflect a fundamental difference between plant and animal pyruvate kinases. It is concluded that control of cytosol pyruvate kinase may be closely related to reactions involved in the assimilation of NH4+.

Placental enzymes of glycolysis, gluconeogenesis and lipogenesis in the diabetic rat and in starvation. Comparison with maternal and foetal liver.

Abstract: The activity of several regulatory enzymes representing the pathways of glycolysis, gluconeogenesis, NADPH generation and lipogenesis was measured in rat placenta maternal and foetal livers on the 20th day of gestation. Streptozotocin diabetes, induced on the 12th day of gestation, or 48 h of fasting did not induce adaptive changes in the activity of placental enzymes while producing a typical insulin deficiency pattern in maternal liver. Foetal liver enzyme activities were unaffected by fasting and in diabetes showed changes suggestive of foetal hyperinsulinaemia. A small increase was observed in the activity of placental pyruvate kinase and a small decrease in that of PEP carboxylase in diabetic and in glucocorticoid-treated rats; these changes were reciprocal to those in the maternal liver and were attributed to hyperglycaemia, as was the increase in placental glycogen. Lack of response to insulin deficiency and to other endocrine alterations indicates that placenta is not sensitive to stimuli which induce adaptive alterations in hepatic enzymes. The only consistent change found in placental enzyme activities was a decrease associated with gestational age.

Bioenergetic Pattern of Isolated Type II Pneumocytes in Air and during Hypoxia

Abstract: The bioenergetic pattern of a cell clone derived from rat lung with ultrastructural and biochemical characteristics like those of type II pneumocytes (T-II-P), has been studied in a tissue culture system. During air cultivation, these cells have a high rate of aerobic and anaerobic glycolysis associated with high activities of two rate-limiting enzymes in glycolysis (pyruvate kinase [PyKi] and phosphofructokinase [PFK]). This is present despite the rates of oxygen consumption and activities of cytochrome oxidase (CyOx) similar to other lung cells. Presumably the high rate of aerobic glycolysis explains the substantial lactate production previously described in lung slices and in the intact perfused lung. Hypoxic cultivation results in a decrease in CyOx. Acute re-exposure to air does not restore the oxygen consumption to normal, presumably as a result of decreased mitochondrial O(2) utilization associated with decreased CyOx activity. As a result, hypoxically cultivated T-II-P cells have a decreased capacity for mitochondrial ATP generation in air as compared to air-cultivated cells. During hypoxia, aerobic and anaerobic glycolysis are further increased as well as the activities of PyKi and PFK. The high rate of glycolysis and high activities of PyKi and PFK in cultivated T-II-P appear to reflect intrinsic genetic regulation. The decreased CyOx activity and increased PyKi and PFK activities in hypoxic T-II-P appear to reflect alterations in enzyme biosynthesis/biodegradation regulated by O(2) availability.