Enzymes of an alternative pathway of glucose metabolism in obligate methanotrophs.
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ABSTRACT:
SUBMITTER: Rozova ON
PROVIDER: S-EPMC8062543 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:1. The occurrence of five enzymes of the pentose phosphate pathway in cell-free preparations of the mucosa of rat small intestine is described. These enzymes were found to be localized mainly in the supernatant fraction (6240000g-min.). 2. The properties of glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase were studied with respect to K(m) values for substrates and NADP(+), pH optima and the effects of p-chloromercuribenzoate and palmitoyl-CoA. Higher total and specific activities of these two dehydrogenases were noted in the proximal half of the small intestine of the rat than in the distal half. 3. The specific activities of glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase in the mucosa of the small intestine of the rat, cat, rabbit and guinea pig were compared. 4. In the rat the specific activities of ribose 5-phosphate isomerase, transketolase and transaldolase were higher in the supernatant fractions from the intestinal mucosa than in those from the liver. 5. The role of the pentose phosphate pathway is discussed in relation to the metabolism of hexose phosphates in the intestinal mucosa.
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Project description:The posttranslational modification (PTM) in protein occurs in a regiospecific manner. In addition, the most commonly occurring PTMs involve similar residues in proteins such as acetylation, ubiquitylation, methylation and sumoylation at the lysine residue and phosphorylation and O-GlcNAc modification at serine/threonine residues. Thus, the possibility of modification sites where two such PTMs may occur in a mutually exclusive manner (ME-PTM) is much higher than known. A recent surge in the identification and the mapping of the commonly occurring PTMs in proteins has revealed that this is indeed the case. However, in what way such ME-PTM sites are regulated and what could be their relevance in the coordinated network of protein function remains to be known. To gain such potential insights in a biological context, we analyzed two most prevalent PTMs on the lysine residue by acetylation and ubiquitylation along with the most abundant PTM in proteins by phosphorylation among enzymes involved in glucose metabolism, a fundamental process in biology. The analysis of the PTM data sets has revealed two important clues that may be intrinsically associated with their regulation and function. First, the most commonly occurring PTMs by phosphorylation, acetylation and ubiquitylation are widespread and clustered in most of the enzymes involved in glucose metabolism; and the prevalence of phosphorylation sites correlates with the number of acetylation and ubiquitylation sites including the ME-modification sites. Second, the prevalence of ME-acetylation/ubiquitylation sites is exceptionally high among enzymes involved in glucose metabolism and have distinct pattern among the subset of enzymes of glucose metabolism such as glycolysis, tricarboxylic acid (TCA) cycle, glycogen synthesis, and the irreversible steps of gluconeogenesis. We hypothesize that phosphorylation including tyrosine phosphorylation plays an important role in the regulation of ME-acetylation/ubiquitylation sites and their similar pattern among the subset of functionally related proteins allows their coordinated regulation in the normal physiology. Similarly their coordinated dysregulation may underlie the disease processes such as reprogrammed metabolism in cancer, obesity, type 2 diabetes, and cardiovascular diseases. Our hypothesis provides an opportunity to understand the regulation of ME-PTMs in proteins and their relevance at the network level and is open for experimental validation.
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Project description:In American Tegumentary Leishmaniasis production of cytokines, reactive oxygen species and nitric oxide (NO) by host macrophages normally lead to parasite death. However, some Leishmania braziliensis strains exhibit natural NO resistance. NO-resistant strains cause more lesions and are frequently more resistant to antimonial treatment than NO-susceptible ones, suggesting that NO-resistant parasites are endowed with specific mechanisms of survival and persistence. To tests this, we analyzed the effect of pro- and antioxidant molecules on the infectivity in vitro of L. braziliensis strains exhibiting polar phenotypes of resistance or susceptibility to NO. In addition, we conducted a comprehensive quantitative mass spectrometry-based proteomics analysis of those parasites. NO-resistant parasites were more infective to peritoneal macrophages, even in the presence of high levels of reactive species. Principal component analysis of protein concentration values clearly differentiated NO-resistant from NO-susceptible parasites, suggesting that there are natural intrinsic differences at molecular level among those strains. Upon NO exposure, NO-resistant parasites rapidly modulated their proteome, increasing their total protein content and glutathione (GSH) metabolism. Furthermore, NO-resistant parasites showed increased glucose analogue uptake, and increased abundance of phosphotransferase and G6PDH after nitrosative challenge, which can contribute to NADPH pool maintenance and fuel the reducing conditions for the recovery of GSH upon NO exposure. Thus, increased glucose consumption and GSH-mediated redox capability may explain the natural resistance of L. braziliensis against NO.
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Project description:1. The pentose phosphate pathway in Krebs ascites cells was investigated for regulatory reactions. For comparison, the glycolytic pathway was studied simultaneously. 2. Activities of the pentose phosphate pathway enzymes were low in contrast with those of the enzymes of glycolysis. The K(m) values of glucose 6-phosphate dehydrogenase for both substrate and cofactor were about four times the reported upper limit for the enzyme from normal tissues. Fructose 1,6-diphosphate and NADPH competitively inhibited 6-phosphogluconate dehydrogenase. 3. About 28% of the hexokinase activity was in the particulate fraction of the cells. The soluble enzyme was inhibited by fructose 1,6-diphosphate and ribose 5-phosphate, but not by 3-phosphoglycerate. The behaviour of the partially purified soluble enzyme in vitro in a system simulating the concentrations of ATP, glucose 6-phosphate and P(i) found in vivo is reported. 4. Kinetics of metabolite accumulation during the transient state after the addition of glucose to the cells indicated two phases of glucose phosphorylation, an initial rapid phase followed abruptly by a slow phase extending into the steady state. 5. Of the pentose phosphate pathway intermediates, accumulation of 6-phosphogluconate, sedoheptulose 7-phosphate and fructose 6-phosphate paralleled the accumulation of glucose 6-phosphate. Erythrose 4-phosphate reached the steady-state concentration by 2min., whereas the pentose phosphates accumulated linearly. 6. The mass-action ratios of the pentose phosphate pathway reactions were calculated. The transketolase reaction was at equilibrium by 30sec. and then progressively shifted away from equilibrium towards the steady-state ratio. The glucose 6-phosphate dehydrogenase was far from equilibrium at all times. 7. Investigation of the flux of [(14)C]glucose carbon confirmed the existence of an operative pentose phosphate pathway in ascites cells, contributing 1% of the total flux in control cells and 10% in cells treated with phenazine methosulphate. 8. The pentose phosphate formed by way of the direct oxidative route and estimated from the (14)CO(2) yields represented 20% of the total accumulated pentose phosphate, the other 80% being formed by the non-oxidative reactions of the pentose phosphate pathway. 9. The pentose phosphate pathway appears to function as two separate pathways, both operating towards pentose phosphate formation. Control of the two pathways is discussed.
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Project description:Gnas is an imprinted gene with multiple gene products resulting from alternative splicing of different first exons onto a common exon 2. These products include stimulatory G protein alpha-subunit (G(s)alpha), the G protein required for receptor-stimulated cAMP production; extralarge G(s)alpha (XLalphas), a paternally expressed G(s)alpha isoform; and neuroendocrine-specific protein (NESP55), a maternally expressed chromogranin-like protein. G(s)alpha undergoes tissue-specific imprinting, being expressed primarily from the maternal allele in certain tissues. Heterozygous mutation of exon 2 on the maternal (E2m-/+) or paternal (E2+/p-) allele results in opposite effects on energy metabolism. E2m-/+ mice are obese and hypometabolic, whereas E2+/p- mice are lean and hypermetabolic. We now studied the effects of G(s)alpha deficiency without disrupting other Gnas gene products by deleting G(s)alpha exon 1 (E1). E1+/p- mice lacked the E2+/p- phenotype and developed obesity and insulin resistance. The lean, hypermetabolic, and insulin-sensitive E2+/p- phenotype appears to result from XLalphas deficiency, whereas loss of paternal-specific G(s)alpha expression in E1+/p- mice leads to an opposite metabolic phenotype. Thus, alternative Gnas gene products have opposing effects on glucose and lipid metabolism. Like E2m-/+ mice, E1m-/+ mice had s.c. edema at birth, presumably due to loss of maternal G(s)alpha expression. However, E1m-/+ mice differed from E2m-/+ mice in other respects, raising the possibility for the presence of other maternal-specific gene products. E1m-/+ mice had more severe obesity and insulin resistance and lower metabolic rate relative to E1+/p- mice. Differences between E1m-/+ and E1+/p- mice presumably result from differential effects on G(s)alpha expression in tissues where G(s)alpha is normally imprinted.
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Project description:1. Glucose-phosphorylating and glucose 6-phosphatase activities, glucose 6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, NADP(+)-linked isocitrate dehydrogenase, ;malic' enzyme and pyruvate carboxylase were assayed in homogenates of normal mouse islets. 2. Two glucose-phosphorylating activities were detected; the major activity had K(m) 0.075mm for glucose and was inhibited by glucose 6-phosphate (non-competitive with glucose) and mannoheptulose (competitive with glucose). The other (minor) activity had a high K(m) for glucose (mean value 16mm) and was apparently not inhibited by glucose 6-phosphate. 3. Glucose 6-phosphatase activity was present in amounts comparable with the total glucose-phosphorylating activity, with K(m) 1mm for glucose 6-phosphate. Glucose was an inhibitor and the inhibition showed mixed kinetics. No inhibition of glucose 6-phosphate hydrolysis was observed with mannose, citrate or tolbutamide. The inhibition by glucose was not reversed by mannoheptulose. 4. 6-Phosphogluconate dehydrogenase had K(m) values of 2.5 and 21mum for NADP(+) and 6-phosphogluconate respectively. 5. Glucose 6-phosphate dehydrogenase had K(m) values of 4 and 22mum for NADP(+) and glucose 6-phosphate. The K(m) for glucose 6-phosphate was considerably below the intra-islet concentration of glucose 6-phosphate at physiological extracellular glucose concentrations. The enzyme had no apparent requirement for cations. Of a number of possible modifiers of glucose 6-phosphate dehydrogenase, only NADPH was inhibitory. The inhibition by NADPH was competitive with NADP(+) and apparently mixed with respect to glucose 6-phosphate. 6. NADP(+)-isocitrate dehydrogenase was present but the islet homogenate contained little, if any, ;malic' enzyme. The presence of pyruvate carboxylase was also demonstrated. 7. The results obtained are discussed with reference to glucose phosphorylation and glucose 6-phosphate oxidation in the intact mouse islet, and the possible nature of the beta-cell glucoreceptor mechanism.
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