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PubMed1978

Essential Sulfhydryl Group in the Transport-catalyzing Protein of the Hexose-Proton Cotransport System of Chlorella.

The polyene antibiotic nystatin transforms the sugar-proton contransport system of Chlorella to a mere facilitated diffusion system. This experimental condition was used to test the sugar-translocating unit of the active uptake system for possible essential sulfhydryl groups. It could be shown that the catalyzed translocation of sugar is sensitive to the sulfhydryl-reactive compound N-ethylmaleimide. Sugar flow by passive leak as induced by the detergent Triton X-100 is not affected by sulfhydryl reagents. These results show that the sugar-translocating carrier protein possesses a sulfhydryl group, which is essential for its function.

Journal Article↗
PubMed1990

Developmental regulation of enzymes of sucrose and hexose metabolism in effective and ineffective soybean nodules.

Soybean (Glycine max) nodules formed by inoculation with either an effective strain or an ineffective (noninvasive, nodule-forming) strain of Bradyrhizobium japonicum were assayed for changes in developmental patterns of carbon metabolic enzymes of the plant nodule cells. Of the enzyme activities measured, only sucrose synthase, glutamine synthetase, and alcohol dehydrogenase were altered in the ineffective nodules relative to the effective nodules. Sucrose synthase and glutamine synthetase activities were greatly reduced, whereas alcohol dehydrogenase activity was elevated. Dark-induced senescence severely affected sucrose synthase but had little, if any, effect on the other enzymes measured. The developmental patterns of the anaerobically induced enzymes, aldolase and alcohol dehydrogenase, were different from those expected, implying that their development is not regulated solely by oxygen deprivation. However, anaerobic treatment of nodules resulted in responses similar to those enzymes in maize. The developmental profiles of the carbon metabolic enzymes suggest that carbohydrates are metabolized via the sucrose synthase and pentose phosphate pathways. This route of carbon metabolism, compared to glycolysis, would reduce the requirement of ATP for carbohydrate catabolism, generate NADPH for biosynthetic reactions, and provide intermediates for plant secondary metabolism.

Journal Article↗
PubMed1978

Glycosylation in vitro of Semliki-Forest-virus and influenza-virus glycoproteins and its suppression by nucleotide-2-deoxy-hexose.

Cell-free enzyme preparations from cultured fibroblasts infected with Semliki forest virus or fowl plague virus (an influenza A virus) incorporate [14C]-mannose into dolichol-phosphate-mannose, lipid-linked oligosaccharides and into endogenous virus-specific glycoproteins. When GDP-2-deoxy-D-[14C]glucose serves as substrate 2-deoxy-D-[14C]glucose is transferred to dolichol phosphate yielding dolichol-monophosphate-2-deoxy-D-[14C]glucose. UDP-2-deoxy-D-[14C]glucose gives rise also to a lipid which, however, is not a polyprenol derivative. The transfer of [14C]mannose to lipid-extractable fractions and glycoproteins in vitro is blocked by GDP-2-deoxy-D-glucose. It can be restored by exogenous dolichol monophosphate only with regard to the formation of dolichol-monophosphate-[14C]mannose-labelled oligosaccharides into glycoproteins. UDP-2-deoxy-D-glucose has no inhibitory effect on transfer reactions of [14C]mannose from GDP-[14C]mannose into various lipid fractions or into glycoprotein. It is concluded therefore, that the inhibition of glycosylation brought about by 2-deoxyglucose in vivo is caused by an interference of its GDP derivative with the formation of a correct lipid-oligosaccharide.

Dolichol Phosphates↗
PubMed1984

Hexose metabolism in pancreatic islets. The phosphorylation of fructose.

Fructose, like glucose, rapidly equilibrates across the plasma membrane of pancreatic islet cells, but is poorly metabolized and is a weak insulin secretagogue in rat pancreatic islets. A possible explanation for such a situation was sought by investigating the modality of fructose phosphorylation in islet homogenates. Several findings indicated that the phosphorylation of fructose is catalyzed by hexokinase, but not fructokinase. First, at variance with the situation found in liver homogenates, the phosphorylation of fructose in the islet homogenate was unaffected by K+ and inhibited by glucose, mannose, glucose 6-phosphate or glucose 1,6-bisphosphate. Second, the Km for fructose was much higher in islets than in liver. Third, in islet homogenates the Km and Vmax for fructose were much higher than those for glucose or mannose phosphorylation, at low aldohexose concentrations, in good agreement with the properties of purified hexokinase. In intact islets fructose augmented the islet content in glucose 6-phosphate sufficiently to cause marked inhibition of its own rate of phosphorylation. These findings may account, in part at least, for the low rate of fructose utilization by rat pancreatic islets.

Animals↗
PubMed1994

Role of the phosphotransferase system in Escherichia coli strains deficient in hexose phosphate transport.

In Escherichia coli, glucose 6-phosphate is transported via the Uhp system which is inducible by glucose 6-phosphate. We showed that, in a uhp-deficient strain, glucose 6-phosphate was dephosphorylated in the periplasm and that the resulting glucose was subsequently transported into the cells via the phosphotransferase system. The uptake of glucose generated from glucose 6-phosphate allowed the bacteria to produce an increased level of cAMP compared to cells grown on non-limiting concentrations of glucose.

Acid Phosphatase↗