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At least 271 records · Page 15Linked to original sources
PubMed1972

The stereochemical structure of disodium DL-glycerol 3-phosphate hexahydrate, the D isomer of which is an inhibitor of triose phosphate isomerase.

The stereochemistry of dl-glycerol 3-phosphate was studied by X-ray-crystallographic techniques. All the bond lengths and angles are within normally accepted limits except the ester bond, which is one of the largest yet noted, being 0.1637nm. The conformation of the molecule is such that an intramolecular hydrogen bond is formed between the hydroxyl group on the beta-carbon atom and the phosphate group. The crystal, which was grown by alcohol diffusion into an aqueous solution, is held together by sodium co-ordination and a complex system of hydrogen bonds. A table of the observed and calculated structure factors, F(obs.) and F(calc.), has been deposited as Supplementary Publication 50010 at the National Lending Library for Science and Technology, Boston Spa, Yorks. LS23 7BQ, U.K., from whom copies can be obtained on the terms indicated in Biochem. J. (1972) 126, 5.

Carbohydrate Epimerases↗
PubMed1986

Limitation of Photosynthesis by Carbon Metabolism : II. O(2)-Insensitive CO(2) Uptake Results from Limitation Of Triose Phosphate Utilization.

The occurrence of O(2)-insensitive photosynthesis at high quantum flux and moderate temperature in Spinacia oleracea was characterized by analytical gas exchange measurements on intact leaves. In addition photosynthetic metabolite pools were measured in leaves which had been rapidly frozen under defined gas conditions. Upon switching to low O(2) in O(2)-insensitive conditions the ATP/ADP ratio fell dramatically within one minute. The P-glycerate pool increased over the same time. Ribulose bisphosphate initially declined, then increased and exceeded the pool size measured in air. The pools of hexose monophosphates and UDPglucose were higher at a partial pressure of O(2) of 21 millibars than at 210 millibars. These results are consistent with the hypothesis that the rate of sucrose synthesis limited the overall rate of assimilation under O(2)-insensitive conditions.

Journal Article↗
PubMed1990

A Model Describing the Regulation of Ribulose-1,5-Bisphosphate Carboxylase, Electron Transport, and Triose Phosphate Use in Response to Light Intensity and CO(2) in C(3) Plants.

A model of the regulation of the activity of ribulose-1,5-bisphosphate carboxylase, electron transport, and the rate of orthophosphate regeneration by starch and sucrose synthesis in response to changes in light intensity and partial pressures of CO(2) and O(2) is presented. The key assumption behind the model is that nonlimiting processes of photosynthesis are regulated to balance the capacity of limiting processes. Thus, at CO(2) partial pressures below ambient, when a limitation on photosynthesis by the capacity of rubisco is postulated, the activities of electron transport and phosphate regeneration are down-regulated in order that the rate of RuBP regeneration matches the rate of RuBP consumption by rubisco. Similarly, at subsaturating light intensity or elevated CO(2), when electron transport or Pi regeneration may limit photosynthesis, the activity of rubisco is downregulated to balance the limitation in the rate of RuBP regeneration. Comparisons with published data demonstrate a general consistency between modelled predictions and measured results.

Journal Article↗
PubMed1989

NMR analysis of site-specific mutants of yeast phosphoglycerate kinase. An investigation of the triose-binding site.

Site-specific mutants of yeast phosphoglycerate kinase have been produced in order to investigate the roles of the 'basic-patch' residues, arginine 168 and histidine 170. The fully-conserved residue, arginine 168, has been replaced with a lysine (R168K) and a methionine (R168M) residue, while the non-conserved histidine 170 has been replaced with an aspartate (H170D). Comparison of the 500-MHz 1H-NMR spectra of the mutant proteins with that of wild-type phosphoglycerate kinase shows that the overall fold of the mutants remains essentially unaltered from that of the native enzyme. Results of NOE experiments indicate that there are only very minor changes in structure in the vicinity of the mutations. These mutations have also led to firm sequence-specific resonance assignments to histidines 62, 167 and 170. NMR studies of 3-phosphoglycerate binding show that decreasing the positive charge in the sequence 168-170 reduces the binding of this substrate (by about 15-fold and 4-fold for mutants R168M and H170D respectively). Mutant R168K binds 3-phosphoglycerate with an affinity about twofold less than that of the native enzyme. Significantly, the activity of mutant H170D, measured at saturating substrate concentrations, is unchanged from that of the wild-type enzyme. This indicates that this residue is not of major importance in the binding or reaction of 3-phosphoglycerate. The observation is in agreement with results obtained for the wild-type enzyme, which indicate that 3-phosphoglycerate interacts most strongly with histidine 62 and least strongly with histidine 170, as would be predicted from the X-ray crystal structure. Substitution of positively charged arginine 168 with neutral methionine (or positively charged lysine) does not cause a detectable change in the pKa values of the neighbouring histidine groups, in as much as they remain below 3. The results reported here indicate that the observed reduction in catalytic efficiency relates less to direct electrostatic effects than to the mutants' inability to undergo 3-phosphoglycerate-induced conformational changes.

Arginine↗
PubMed1978

Mode of action of alpha-chlorohydrin as a male anti-fertility agent. Inhibition of the metabolism of ram spermatozoa by alpha-chlorohydrin and location of block in glycolysis.

1. The effect of alpha-chlorohydrin on the metabolism of glycolytic and tricarboxylate-cycle substrates by ram spermatozoa was investigated. The utilization and oxidation of fructose and triose phosphate were much more sensitive to inhibition by alpha-chlorohydrin (0.1-1.0mm) than lactate or pyruvate. Inhibition of glycolysis by alpha-chlorohydrin is concluded to be between triose phosphate and pyruvate formation. Oxidation of glycerol was not as severely inhibited as that of the triose phosphate. This unexpected finding can be explained in terms of competition between glycerol and alpha-chlorohydrin. A second, much less sensitive site, of alpha-chlorohydrin inhibition appears to be associated with production of acetyl-CoA from exogenous and endogenous fatty acids. 2. Measurement of the glycolytic intermediates after incubation of spermatozoal suspensions with 15mm-fructose in the presence of 3mm-alpha-chlorohydrin showed a ;block' in the conversion of glyceraldehyde 3-phosphate into 3-phosphoglycerate. alpha-Chlorohydrin also caused conversion of most of the ATP in spermatozoa into AMP. After incubation with 3mm-alpha-chlorohydrin, glyceraldehyde 3-phosphate dehydrogenase and triose phosphate isomerase activities were decreased by approx. 90% and 80% respectively, and in some experiments aldolase was also inhibited. Other glycolytic enzymes were not affected by a low concentration (0.3mm) of alpha-chlorohydrin. Loss of motility of spermatozoa paralleled the decrease in glyceraldehyde 3-phosphate dehydrogenase activity. alpha-Chlorohydrin, however, did not inhibit glyceraldehyde 3-phosphate dehydrogenase or triose phosphate isomerase in sonicated enzyme preparations when added to the assay cuvette. 3. Measurement of intermediates and glycolytic enzymes in ejaculated spermatozoa before, during and after injection of rams with alpha-chlorohydrin (25mg/kg body wt.) confirmed a severe block in glycolysis in vivo at the site of triose phosphate conversion into 3-phosphoglycerate within 24h of the first injection. Glyceraldehyde 3-phosphate dehydrogenase activity was no longer detectable and both aldolase and triose phosphate isomerase were severely inhibited. Spermatozoal ATP decreased by 92% at this time, being quantitatively converted into AMP. At 1 month after injection of alpha-chlorohydrin glycolytic intermediate concentrations returned to normal in the spermatozoa but ATP was still only 38% of the pre-injection concentration. Motility of spermatozoa was, however, as good as during the pre-injection period. The activity of the inhibited enzymes also returned to normal during the recovery period and 26 days after injection were close to pre-injection values. 4. An unknown metabolic product of alpha-chlorohydrin is suggested to inhibit glyceraldehyde 3-phosphate dehydrogenase and triose phosphate isomerase of spermatozoa. This results in a lower ATP content, motility and fertility of the spermatozoa. Glycidol was shown not to be an active intermediate of alpha-chlorohydrin in vitro.

Animals↗