Poly-β-hydroxybutyrate biosynthesis and the regulation of glucose metabolism in Azotobacter beijerinckii

Azotobacter beijerinckii possesses the enzymes of both the Entner-Doudoroff and the oxidative pentose phosphate cycle pathways of glucose catabolism and both pathways are subject to feedback inhibition by products of glucose oxidation. The allosteric glucose 6-phosphate dehydrogenase utilizes both NADP(+) and NAD(+) as electron acceptors and is inhibited by ATP, ADP, NADH and NADPH. 6-Phosphogluconate dehydrogenase (NADP-specific) is unaffected by adenosine nucleotides but is strongly inhibited by NADH and NADPH. The formation of pyruvate and glyceraldehyde 3-phosphate from 6-phosphogluconate by the action of the Entner-Doudoroff enzymes is inhibited by ATP, citrate, isocitrate and cis-aconitate. Glyceraldehyde 3-phosphate dehydrogenase is unaffected by adenosine and nicotinamide nucleotides but the enzyme is non-specific with respect to NADP and NAD. Citrate synthase is strongly inhibited by NADH and the inhibition is reversed by the addition of AMP. Isocitrate dehydrogenase, a highly active NADP-specific enzyme, is inhibited by NADPH, NADH, ATP and by high concentrations of NADP(+). These findings are discussed in relation to the massive synthesis of poly-beta-hydroxybutyrate that occurs under certain nutritional conditions. We propose that synthesis of this reserve material, to the extent of 70% of the dry weight of the organism, serves as an electron and carbon ;sink' when conditions prevail that would otherwise inhibit nitrogen fixation and growth.     

The pentose phosphate pathway of glucose metabolism. Measurement of the non-oxidative reactions of the cycle

Methods for the quantitative determination of ribose 5-phosphate isomerase, ribulose 5-phosphate 3-epimerase, transketolase and transaldolase in tissue extracts are described. The determinations depend on the measurement of glyceraldehyde 3-phosphate by using the coupled system triose phosphate isomerase, α-glycero-phosphate dehydrogenase and NADH. By using additional purified enzymes transketolase, ribose 5-phosphate isomerase and ribulose 5-phosphate epimerase conditions could be arranged so that each enzyme in turn was made rate-limiting in the overall system. Transaldolase was measured with fructose 6-phosphate and erythrose 4-phosphate as substrates, and again glyceraldehyde 3-phosphate was measured by using the same coupled system. Measurements of the activities of the non-oxidative reactions of the pentose phosphate pathway were made in a variety of tissues and the values compared with those of the two oxidative steps catalysed by glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase.     

Utilization of Glucose by Clostridium thermocellum: Presence of Glucokinase and Other Glycolytic Enzymes in Cell Extracts

Clostridium thermocellum was shown to ferment glucose in a medium containing salts and 0.5% yeast extract. An active glucokinase was obtained with improved conditions for growth, assay, and preparation of cell extracts. Cell extracts appear to contain a glucokinase inhibitor that interferes with the assays at high protein concentrations. Glucokinase activity is stimulated about 60% by pretreatment with dithiothreitol. Little or no fructokinase or mannokinase activity was detected in cell extracts. The absence of glucokinase in mannitol-grown cells, the increase in glucokinase activity upon incubation of cell suspensions with glucose, and the lack of increase in activity when chloramphenical is added are evidence that glucokinase is an inducible enzyme. The following enzymes were detected in cell extracts (the enzyme activities are shown in parentheses are micromoles per minute per milligram or protein at 27 C): glucokinase (0.48), phosphoglucose isomerase (0.73), fructose 6-phosphate kinase (0.24), fructose diphosphate aldolase (0.59), glyceraldehyde 3-phosphate dehydrogenase (0.53), triose phosphate isomerase (0.13), phosphoglycerate kinase (0.20), phosphoglycerate mutase (0.20), enolase (0.28), pyruvic kinase (0.13), and lactic dehydrogenase (0.13). Glucose 6-phosphate dehydrogenase activity was absent or very low (0.0002) and 6-phosphogluconate dehydrogenase activity also was relatively low (0.015). From these data, it is proposed that carbohydrate metabolism in C. thermocellum proceeds by the Embden-Meyerhof pathway.     

Enzymatic analysis of the pathways of glucose catabolism and gluconeogenesis in Pseudomonas citronellolis

Extracts of Pseudomonas citronellolis cells grown on glucose or gluconate possessed all the enzymes of the Entner-Doudoroff pathway. Gluconokinase and either or both 6-phosphogluconate dehydratase and KDPG aldolase were induced by growth on these substrates. Glucose and gluconate dehydrogenases and 6-phosphofructokinase were not detected. Thus catabolism of glucose proceeds via an inducible Entner-Doudoroff pathway. Metabolism of glyceraldehyde 3-phosphate apparently proceeded via glyceraldehyde 3-phosphate dehydrogenase, phosphoglycerate kinase, phosphoglycerate mutase, enolase and pyruvate kinase. These same enzymes plus triose phosphate isomerase were present in lactate-grown cells indicating that synthesis of triose phosphates from gluconeogenic substrates also occurs via this pathway. Extracts of lactate grown-cells possessed fructose diphosphatase and phosphohexoisomerase but apparently lacked fructose diphosphate aldolase thus indicating either the presence of an aldolase with unusual properties or requirements or an alternative pathway for the conversion of triose phosphate to fructose disphosphate. Cells contained two species of glyceraldehyde 3-phosphate dehydrogenase, one an NAD-dependent enzyme which predominated when the organism was grown on glycolytic substrates and the other, an NADP-dependent enzyme which predominated when the organism was grown on gluconeogenic substrates.     

Activities of enzymes of the oxidative and the reductive pentose phosphate pathways in heterocysts of a blue-green alga

Preparations of heterocysts of Anabaena cylindrica Lemm. had 7- to 8-fold higher activities of glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase, 2-fold more hexokinase activity, and 0.02 to 0.06 times as much ribulose diphosphate carboxylase and glyceraldehyde 3-phosphate dehydrogenase activities as did whole filaments per milligram soluble protein in cell-free extracts. Time courses of solubilization of glucose 6-phosphate dehydrogenase activity indicated that heterocysts contain 74 to 80% of the total activity of this enzyme in filaments.     

Oxidation of C1-compounds in Pseudomonas C.

Extracts of Pseudomonas C grown on methanol as a sole carbon and energy source contain a methanol dehydrogenase activity which can be coupled to phenazine methosulfate. This enzyme catalyzes two reactions namely the conversion of methanol to formaldehyde (phenazine methosulfate coupled) and the oxidation of formaldehyde to formate (2,6-dichloroindophenol-coupled). Activities of glutathione-dependent formaldehyde dehydrogenase (NAD+) and formate dehydrogenase (NAD+) were also detected in the extracts. The addition of D-ribulose 5-phosphate to the reaction mixtures caused a marked increase in the formaldehyde-dependent reduction of NAD+ or NADP+. In addition, the oxidation of [14C]formaldehyde to CO2, by extracts of Pseudomonas C, increased when D-ribulose 5-phosphate was present in the assay mixtures. The amount of radioactivity found in CO2, was 6;8-times higher when extracts of methanol-grown Pseudomonas C were incubated for a short period of time with [1-14C]glucose 6-phosphate than with [U-14C]glucose 6-phosphate. These data, and the presence of high specific activities of hexulose phosphate synthase, phosphoglucoisomerase, glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase indicate that in methanol-grown Pseudomonas C, formaldehyde carbon is oxidized to CO2 both via a cyclic pathway which includes the enzymes mentioned and via formate as an oxidation intermediate, with the former predominant.     

Enzymes of glucose metabolism in Frankia sp.

Enzymes of glucose metabolism were assayed in crude cell extracts of Frankia strains HFPArI3 and HFPCcI2 as well as in isolated vesicle clusters from Alnus rubra root nodules. Activities of the Embden-Meyerhof-Parnas pathway enzymes glucokinase, phosphofructokinase, and pyruvate kinase were found in Frankia strain HFPArI3 and glucokinase and pyruvate kinase were found in Frankia strain HFPCcI2 and in the vesicle clusters. An NADP+-linked glucose 6-phosphate dehydrogenase and an NAD-linked 6-phosphogluconate dehydrogenase were found in all of the extracts, although the role of these enzymes is unclear. No NADP+-linked 6-phosphogluconate dehydrogenase was found. Both dehydrogenases were inhibited by adenosine 5-triphosphate, and the apparent Km's for glucose 6-phosphate and 6-phosphogluconate were 6.86 X 10(-4) and 7.0 X 10(-5) M, respectively. In addition to the enzymes mentioned above, an NADP+-linked malic enzyme was detected in the pure cultures but not in the vesicle clusters. In contrast, however, the vesicle clusters had activity of an NAD-linked malic enzyme. The possibility that this enzyme resulted from contamination from plant mitochondria trapped in the vesicle clusters could not be discounted. None of the extracts showed activities of the Entner-Doudoroff enzymes or the gluconate metabolism enzymes gluconate dehydrogenase or gluconokinase. Propionate- versus trehalose-grown cultures of strain HFPArI3 showed similar activities of most enzymes except malic enzyme, which was higher in the cultures grown on the organic acid. Nitrogen-fixing cultures of strain HFPArI3 showed higher specific activities of glucose 6-phosphate and 6-phosphogluconate dehydrogenases and phosphofructokinase than ammonia-grown cultures.     

Ethanol production by thermophilic bacteria: biochemical basis for ethanol and hydrogen tolerance in Clostridium thermohydrosulfuricum.

The metabolic and enzymatic bases for growth tolerance to ethanol (4%) and H2 (2 atm [1 atm = 101.29 kPa]) fermentation products in Clostridium thermohydrosulfuricum were compared in a sensitive wild-type strain and an insensitive alcohol-adapted strain. In the wild-type strain, ethanol (4%) and H2 (2 atm) inhibited glucose but not pyruvate fermentation parameters (growth and end product formation). Inhibition of glucose fermentation by ethanol (4%) in the wild-type strain was reversed by addition of acetone (1%), which lowered H2 and ethanol production while increasing isopropanol and acetate production. Pulsing cells grown in continuous culture on glucose with 5% ethanol or 1 atm of H2 significantly raised the NADH/NAD ratio in the wild-type strain but not in the alcohol-adapted strain. Analysis of key oxidoreductases demonstrated that the alcohol-adapted strain lacked detectable levels of reduced ferredoxin-linked NAD reductase and NAD-linked alcohol dehydrogenase activities which were present in the wild-type strain. Differences in the glucose fermentation product ratios of the two strains were related to differences in lactate dehydrogenase and hydrogenase levels and sensitivity of glyceraldehyde 3-phosphate dehydrogenase activity to NADH inhibition. A biochemical model is proposed which describes a common enzymatic mechanism for growth tolerance of thermoanaerobes to moderate concentrations of both ethanol and hydrogen.     

Oxidative Enzymes and Pathways of Hexose and Triose Metabolism in Chlorella

Cell-free preparations of Chlorella pyrenoidosa Chick, van Niel's strain, were assayed for oxidative enzymes, utilizing isotopic and spectrophotometric techniques. The enzyme activity of heterotrophic and autotrophic cells was compared. The study was divided into categories, one concerned with the spectrophotometric detection of enzymes involved in the initial reactions of glycolysis and the hexose monophosphate shunt, and the other with the direct oxidation of glucose as compared with that oxidized via glycolysis. The reduction of pyridine nucleotides in crude extracts was studied with glucose, glucose-6-phosphate, 6-phosphogluconate, and fructose-1-6-diphosphate as substrates. Enzymes detected in both heterotrophic and autotrophic cells were hexokinase, fructose-diphosphate-aldolase, NAD-linked 3-phosphoglyceraldchyde dehydrogenase, glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, and a NADP-linked 3-phosphoglyceraldchyde dehydrogenase. In addition to isotopic studies designed to make an appraisal of the hexose monophosphate shunt, a comparison of the rate of reduction of NADP by glucose-6-phosphate and 6-phosphogluconate in relation to the reduction of NAD by 3-phosphoglyceraldehyde was made in light- and dark-grown cells. The rate of reduction of NADP appeared to be lowered in the light-grown cells, suggesting, as did also the isotopic studies, that the hexose monophosphate shunt is less active in autotrophic metabolism than in heterotrophic metabolism.     

Activity and androgenic control of glycolytic enzymes in the epididymis and epididymal spermatozoa of the rat.

1. Procedures were developed for the extraction and assay of glycolytic enzymes from the epididymis and epididymal spermatozoa of the rat. 2. The epididymis was separated into four segments for analysis. When rendered free of spermatozoa by efferent duct ligation, regional differences in enzyme activity were apparent. Phosphofructokinase, glycerol phosphate dehydrogenase and glucose 6-phosphate dehydrogenase were more active in the proximal regions of the epididymis, whereas hexokinase, lactate dehydrogenase and phosphorylase were more active in the distal segment. These enzymes were less active in the epididymis of castrated animals and less difference was apparent between the proximal and distal segments. However, the corpus epididymidis from castrated rats had lower activities of almost all enzymes compared with other epididymal segments. 3. Spermatozoa required sonication to obtain satisfactory enzyme release. Glycolytic enzymes were more active in spermatozoa than in epididymal tissue, being more than 10 times as active in the case of hexokinase, phosphoglycerate kinase and phosphoglycerate mutase. 4. The specific activities of a number of enzymes in the epididymis were dependent on the androgen status of the animal. These included hexokinase, phosphofructokinase, aldolase, glyceraldehyde phosphate dehydrogenase, phosphoglycerate kinase, pyruvate kinase, glycerol phosphate dehydrogenase, glucose 6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase and phosphorylase. 5. The caput and cauda epididymidis differed in the extent to which enzyme activities changed in response to an altered androgen status. The most notable examples were hexokinase, phosphofructokinase, aldolase, phosphoglycerate kinase, 6-phosphogluconate dehydrogenase and phosphorylase.     

Multiple Forms of Pseudomonas multivorans Glucose-6-Phosphate and 6-Phosphogluconate Dehydrogenases: Differences in Size, Pyridine Nucleotide Specificity, and Susceptibility to Inhibition by Adenosine 5′-Triphosphate

Two major species of glucose-6-phosphate dehydrogenase (EC 1.1.1.49) differing in size, pyridine nucleotide specificity, and susceptibility to inhibition by adenosine 5'-triphosphate (ATP) were detected in extracts of Pseudomonas multivorans (which has recently been shown to be synonymous with the species Pseudomonas cepacia) ATCC 17616. The large species (molecular weight ca. 230,000) was active with nicotinamide adenine dinucleotide (NAD) or nicotinamide adenine dinucleotide phosphate (NADP) and was markedly inhibited by ATP, which decreased its affinity for glucose-6-phosphate and for pyridine nucleotides. This form of the enzyme exhibited homotropic effects for glucose-6-phosphate. The small species (molecular weight ca. 96,000) was active with NADP but not with NAD, was not inhibited by ATP, and exhibited no homotropic effects for glucose-6-phosphate. Under certain conditions multiplicity of 6-phosphogluconate dehydrogenase (EC 1.1.1.43) activities was also noted. One form of the enzyme (80,000 molecular weight) was active with either NAD or NADP and was inhibited by ATP, which decreased its affinity for 6-phosphogluconate. The other form (120,000 molecular weight) was highly specific for NADP and was not susceptible to inhibition by ATP. Neither form of the enzyme exhibited homotropic effects for 6-phosphogluconate. The possible relationships between the different species of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase are discussed.     

Studies on the function of proplastids in the metabolism of in vitro-cultured tobacco cells IV. Gluconeogenetic pathway

Proplastids of in vitro-cultured tobacco cells were shown tocontain the enzymes of the gluconeogenetic pathway from triosephosphate to glucose 1-phosphate. No significant activitiesof NADP-dependent glyceraldehyde 3-phosphate dehydrogenase andhexokinase were detected. Ribulose 1,5-diphosphate carboxylaseactivity was significant but very low. It was concluded thatthe gluconeogenetic pathway plays roles in the production ofglucose 6-phosphate as the substrate to produce NADPH₂ by glucose6-phosphate and 6-phosphogluconate dehydrogenases, as well asin starch formation. (Received May 19, 1977; )     

Reactions of d-glyceraldehyde 3-phosphate dehydrogenase facilitated by oxidized nicotinamide–adenine dinucleotide

Transient kinetic methods have been used to study the influence of NAD(+) on the rate of elementary processes of the reversible oxidative phosphorylation of d-glyceraldehyde 3-phosphate catalysed by d-glyceraldehyde 3-phosphate dehydrogenase. In the pH range 5-8 NAD(+) is bound to the enzyme during the following elementary processes of the mechanism: phosphorolysis of the acyl-enzyme, its formation from 1,3-diphosphoglycerate and the enzyme and the formation and breakdown of the glyceraldehyde 3-phosphate-enzyme complex. The rates of these four elementary processes only equal or exceed the turnover rate of the enzyme when NAD(+) is bound and are as much as 10(4) times the rates in the absence of NAD(+). Autocatalysis of the reductive dephosphorylation of 1,3-diphosphoglycerate occurs when glyceraldehyde 3-phosphate release is rate determining because NAD(+) is a reaction product. An important feature of the enzyme mechanism is that the negative-free-energy change of a chemical reaction, acyl-enzyme formation, is linked in a simple way to the positive-free-energy change of a dissociation reaction, NAD(+) release.     

Degradation of glucose-metabolizing enzymes in the rat small intestine during starvation

1. The degradation rates and half-lives of hexokinase, 6-phosphogluconate dehydrogenase, lactate dehydrogenase, pyruvate kinase, glucose 6-phosphate dehydrogenase, phosphoglycerate kinase and aldolase were calculated from measurements of the decline in activities of these enzymes in rat small intestine during starvation. 2. The half-lives of the enzymes are: hexokinase, 5.7h; 6-phosphogluconate dehydrogenase, 7.6h; glucose 6-phosphate dehydrogenase, 6.0h; pyruvate kinase, 8.9h; lactate dehydrogenase, 8.7h; phosphoglycerate kinase, 8.7h; aldolase, 5.1h. 3. The significance of the results is discussed with respect to the regulation of enzyme concentrations in response to changes in diet.     

Effect of sequestering and reducing agents on stabilization of plant dehydrogenase activity in crude extracts

Initial and long-term loss of dehydrogenase activity in crude extracts of herbaceous, and, especially, of woody tissue occur partially because of the inhibitory influence of phenolics. In addition, oxidation of phenols by phenolase results in subsequent enzyme oxidation. Preparation of crude extracts with insoluble PVP, in comparison with anion exchange resins or celluloses, best decreases phenolic concentrations and least decreases dehydrogenase activity in crude extracts. However, removal of phenolics during tissue homogenation does not maximize dehydrogenase activity. Therefore, other methods must be used to stabilize dehydrogenase activity. Sodium ethylenediaminetetracetic acid or sodium azide promoted activity of both purified mushroom and crude plant phenolases. Quinone reduction with diethyldithiocarbamate (DIECA) or mercaptoethanol eliminated apparent phenolase activity, but DIECA inhibited dehydrogenase activity. Elevated concentrations of EtSH diminished initial decay of dehydrogenase activity. Combined use of EtSH and insoluble PVP further stabilized 6-phosphogluconate, glucose 6-phosphate, and malate dehydrogenase, but not glyceraldehyde 3-phosphate dehydrogenase.     

Influences of intracellular pyridine nucleotide redox states on fatty acid synthesis in isolated rat hepatocytes.

The regulation of fatty acid synthesis, measured by ³H₂O incorporation into fatty acids, was studied in hepatocytes from rats meal-fed a high carbohydrate diet. Ca²⁺ increased fatty acid synthesis, which became maximal at physiological concentrations of Ca²⁺. Ethanol markedly inhibited fatty acid synthesis. Maximum inhibition was reached at 4 mm ethanol. However, ethanol did not decrease lipogenesis in the presence of pyruvate. dl-3-Hydroxybutyrate increased fatty acid synthesis. Acetoacetate decreased lipogenesis when used alone and reversed the effect of dl-3-hydroxybutyrate when both were added. dl-3-Hydroxybutyrate moderately decreased flux through the pyruvate dehydrogenase system and markedly inhibited citric acid cycle flux. By measurement of glycolytic intermediates, two ethanol-induced crossover points were observed: one between fructose 6-phosphate and fructose 1,6-diphosphate and the other between glyceraldehyde 3-phosphate and 1,3-diphosphoglycerate. The concentrations of pyruvate and citrate were decreased by ethanol and increased by dl-3-hydroxybutyrate. Aminooxyacetate and l-cycloserine inhibited fatty acid synthesis and these effects were overcome by dl-3-hydroxybutyrate. Results indicate that in hepatocytes in a metabolic state favoring a high rate of lipogenesis, production of reducing equivalents in the cytosol via ethanol metabolism inhibits fatty acid synthesis from glucose by inhibition of both phosphofructokinase and glyceraldehyde 3-phosphate dehydrogenase and by promoting reduction of pyruvate to lactate. Production of reducing equivalents in the mitochondria via dl-3-hydroxybutyrate enhances fatty acid synthesis in liver cells by altering the partition of citrate between oxidation in the citric acid cycle and conversion to fatty acids in favor of the latter pathway. These interactions indicate the importance of the intracellular pyridine nucleotide redox states in the rate control of hepatic fatty acid synthesis.     

Changes in activity of some enzymes involved in glucose utilization and formation in developing rat liver

1. The activities of some enzymes involved in both the utilization of glucose (pyruvate kinase, ATP citrate lyase, NADP-specific malate dehydrogenase, glucose 6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase and NADP-specific isocitrate dehydrogenase, all present in the supernatant fraction of liver homogenates) and the formation of glucose by gluconeogenesis (glucose 6-phosphatase in the whole homogenate and fructose 1,6-diphosphatase, phosphopyruvate carboxylase, NAD-specific malate dehydrogenase and fumarase in the supernatant fraction) have been determined in rat liver around birth and in the postnatal period until the end of weaning. 2. The activities of those enzymes involved in the conversion of glucose into lipid are low during the neonatal period and increase with weaning. NADP-specific malate dehydrogenase first appears and develops at the beginning of the weaning period. 3. The marked increase in cytoplasmic phosphopyruvate carboxylase activity at birth is probably the major factor initiating gluconeogenesis at that time. 4. The results are discussed against the known changes in dietary supplies and the known metabolic patterns during the period of development.     

Degradation of endogenous fructose during catabolism of sucrose and mannitol in halophilic archaebacteria

Metabolism of fructose arising endogenously from sucrose or mannitol was studied in halophilic archaebacteria Haloarcula vallismortis and Haloferax mediterranei. Activities of the enzymes of Embden-Meyerhof-Parnas (EMP) pathway, Entner-Doudoroff (ED) pathway and Pentose Phosphate (PP) pathway were examined in extracts of cells grown on sucrose or mannitol and compared to those grown on fructose and glucose. Sucrase and NAD-specific mannitol dehydrogenase were induced only when sucrose or mannitol respectively were the growth substrates. Endogenously arising fructose was metabolised in a manner similar to that for exogenously supplied fructose i.e. a modified EMP pathway initiated by ketohexokinase. While the enzymes for modified EMP pathway viz. ketohexokinase, 1-phosphofructokinase and fructose 1,6-bisphosphate aldolase were present under all growth conditions, their levels were elevated in presence of fructose. Besides, though fructose 1,6-bisphosphatase, phosphohexoseisomerase and glucose 6-phosphate dehydrogenase were present, the absence of 6-phosphogluconate dehydratase precluded routing of fructose through ED pathway, or through PP pathway directly as 6-phosphogluconate dehydrogenase was lacking. Fructose 1,6-bisphosphatase plays the unusual role of a catabolic enzyme in supporting the non-oxidative part of PP pathway. However the presence of constitutive levels of glucose dehydrogenase and 2-keto 3-deoxy 6-phosphogluconate aldolase when glucose or sucrose were growth substrates suggested that glucose breakdown took place via the modified ED pathway.Abbreviations EMP Embden Meyerhof Parnas - ED Entner Doudoroff - PP pentose phosphate - KHK ketohexokinase - 1-PFK 1-phosphofructokinase - PEP-PTS phosphoenolpyruvate phosphotransferase - 6-PFK 6-phosphofructokinase - FBPase fructose 1,6-bisphosphatase - PHI phosphohexoseisomerase - G6P-DH glucose 6-phosphate dehydrogenase - 6PG-DH 6-phosphogluconate dehydrogenase - GAPDH glyceraldehyde 3-phosphate dehydrogenase - FIP fructose 1-phosphate - GSH reduced glutathione - 2-ME -mercaptoethanol - FBP fructose 1,6-bisphosphate - KDPG 2-keto 3-deoxy 6-phosphogluconate - F6P fructose 6-phosphatez     

Enzymes of glycolysis and the pentose phosphate pathway during development of the rabbit stomach worm Obeliscoides cuniculi

The activities of glycolytic and other enzymes of carbohydrate metabolism were measured in free-living and parasitic stages of the rabbit stomach worm Obeliscoides cuniculi. Glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, phosphoglucomutase, hexokinase, glucosephosphate isomerase, phosphofructokinase, aldolase, triosephosphate isomerase, α-glycerophosphatase, glyceraldehyde-3-phosphate dehydrogenase, phosphoglycerate kinase, phosphoglycerate mutase, enolase, pyruvate kinase, phosphoenol pyruvate carboxykinase, lactate dehydrogenase, alcohol dehydrogenase, and glucose-6-phosphatase activities were present in worms recovered 14, 20 and 190 days postinfection.The presence of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase, and glucose-6-phosphatase indicates the possible function of a pentose phosphate pathway and a capacity for gluconeogenesis, respectively, in these worms.The ratio of pyruvate kinase (PK) to phosphoenol pyruvate carboxykinase (PEPCK) less than I in parasitic stages suggests that their most active pathway is that fixing CO₂ into phosphoenol pyruvate to produce oxaloacetate.Low levels of glucose-6-phosphate dehydrogenase, triosephosphate isomerase, PEPCK and PK were recorded in infective third-stage larvae stored at 5°C for 5 and 12 mos. The ratio of PK to PEPCK greater than 1 indicates that infective larvae preferentially utilize a different terminal pathway than the parasitic stages.