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R Bartrons

Publications and source records attributed to R Bartrons.

101 records · Page 6Linked to original sources
PubMed1983

Hormonal control of fructose 2,6-bisphosphate concentration in isolated rat hepatocytes.

The ability of glucagon and of adrenaline to affect the concentration of fructose 2,6-bisphosphate in isolated hepatocytes was re-investigated because of important discrepancies existing in the literature. We were unable to detect a significant difference in the sensitivity of the hepatocytes with regard to the effect of glucagon to initiate the interconversion of phosphorylase, pyruvate kinase, 6-phosphofructo-2-kinase and fructose 2,6-bisphosphatase, and also to cause the disappearance of fructose 2,6-bisphosphate. In contrast, we have observed differences in the time-course of these various changes, since the interconversions of phosphorylase and of pyruvate kinase were at least twice as fast as those of 6-phosphofructo-2-kinase and of fructose 2,6-bisphosphatase. When measured in a cell-free system in the presence of MgATP, the cyclic AMP-dependent interconversion of pyruvate kinase was 5-10-fold more rapid than those of 6-phosphofructo-2-kinase and of fructose 2,6-bisphosphatase. These data indicate that 6-phosphofructo-2-kinase and fructose 2,6-bisphosphatase are relatively poor substrates for cyclic AMP-dependent protein kinase; they also support the hypothesis that the two catalytic activities belong to a single protein. Adrenaline had only a slight effect on the several parameters under investigation, except for the activation of phosphorylase. In the absence of Ca2+ ions from the incubation medium, however, adrenaline had an effect similar to that of glucagon.

Animals↗
PubMed1983

Metabolism of glycerate-2,3-P2--IV. Effect of Hg2+ on the enzymes involved in the metabolism of glycerate-2,3-P2 in pig skeletal muscle.

Type M phosphoglycerate mutase and skeletal muscle bisphosphoglycerate synthase-phosphatase from pig are similarly affected by Hg2+. Both enzymes lose the phosphoglycerate mutase and the glycerate-2,3-P2 synthase activities, and increase the glycerate-2,3-P2 phosphatase activity upon Hg2+-treatment. In contrast, bisphosphoglycerate phosphatase from pig skeletal muscle is inactivated by Hg2+. These results confirm the similarity between phosphoglycerate mutase and bisphosphoglycerate synthase-phosphatase. In addition they support the existence of separate binding sites for monophosphoglycerates and for bisphosphoglycerates at the phosphoglycerate mutase active site.

2,3-Diphosphoglycerate↗
PubMed1982

Purification and characterization of phosphoglycerate mutase isozymes from pig heart.

The three isozymes of phosphoglycerate mutase from pig heart have been purified to homogeneity. The isozymes have a molecular weight of 57000 as determined by gel-filtration chromatography. Discontinuous gel electrophoresis in the presence of sodium dodecyl sulfate yields a single band with a molecular weight of 29000, indicating that the isozymes are dimers composed of subunits of similar mass. Hybridization experiments show that the three isozymes result from homodimeric and heterodimeric combinations of two different subunits. The two types of subunit differ in their heat lability and in the presence of -SH groups essential for enzymatic activity. No remarkable differences exist in the kinetic constants of the purified isozymes. The kinetic pattern is consistent with a 'ping-pong' mechanism. The homogeneous preparations of the three isozymes show intrinsic glycerate-2,3-P2 synthase activity and glycerate-2,3-P2 phosphatase activity which can be stimulated by glycolate-2-P.

Animals↗
PubMed1982

Effect of vanadate on the formation and stability of the phosphoenzyme forms of 2,3-bisphosphoglycerate-dependent phosphoglycerate mutase and of phosphoglucomutase.

2,3-Bisphosphoglycerate-dependent phosphoglycerate mutase (2,3-bisphospho-D-glycerate:2-phospho-D-glycerate phosphotransferase, EC 2.7.5.3) and phosphoglucomutase (alpha-D-glucose-1,6-bisphosphate:alpha -D-glucose-1-phosphate phosphotransferase, EC 2.7.5.1), which are markedly inhibited by vanadate, possess a ping-pong mechanism involving an intermediate phosphoenzyme. The formation and the stability of these phosphoenzymes have been examined spectrophotometrically in the absence of vanadate. Vanadate does not inhibit the phosphorylation of either mutase by its cofactor. The instability of the phosphoenzyme form of phosphoglycerate mutase increases in the presence of vanadate, but the stability of the phosphorylated phosphoglucomutase is not affected.

2,3-Diphosphoglycerate↗
PubMed1982

Phylogeny and ontogeny of the phosphoglycerate mutases--IV. Distribution of glycerate-2,3-P2 dependent and independent phosphoglycerate mutases in algae, fungi, plants and animals.

1. The distribution of the glycerate-2,3-P2 dependent and independent phosphoglycerate mutases (PGM) has been studied in more than eighty species. 2. PGM activity in the extracts has been measured in the presence and in the absence of glycerate-2,3-P2, at pH 7.5 and at pH 8.5. 3. All samples with glycerate-2,3-P2 dependent PGM possess higher activity at pH 7.5 than at pH 8.5. In contrast, samples with glycerate-2,3-P2 independent PGM possess lower activity at pH 7.5 than at pH 8.5. 4. In algae and fungi both glycerate-2,3-P2 dependent and independent PGM have been found. 5. In plants only glycerate-2,3-P2 independent PGM has been detected. 6. In animals both types of PGM are present. Independent PGM activity is present in sponges, coelenterates, myriapods, arachnids and echinoderms. Glycerate-2,3-P2 dependent PGM is present in platyhelminths, mollusks, annelids, crustaceans, insects and vertebrates.

2,3-Diphosphoglycerate↗
PubMed1982

A kinetic study of pyrophosphate: fructose-6-phosphate phosphotransferase from potato tubers. Application to a microassay of fructose 2,6-bisphosphate.

Pyrophosphate : fructose-6-phosphate phosphotransferase (PPi-PFK) has been purified 150-fold from potato tubers and the kinetic properties of the purified enzyme have been investigated both in the forward and the reverse direction. Saturation curves for fructose 6-phosphate and also for fructose 1,6-bisphosphate were sigmoidal whereas those for PPi and Pi were hyperbolic. In the presence of fructose 2,6-bisphosphate, the affinity for fructose 6-phosphate and for fructose 1,6-bisphosphate were greatly increased and the kinetics became Michaëlian. The effect of fructose 2,6-bisphosphate was increased by the presence of fructose 6-phosphate and decreased by the presence of Pi. Consequently, the Ka for fructose 2,6-bisphosphate was as low as 5 nM for the forward reaction and reached 150 nM for the reverse reaction. On the basis of these properties, a procedure allowing one to measure fructose 2,6-bisphosphate in amounts lower than a picomole, is described.

Fructosediphosphates↗
PubMedDate not supplied

Detection of mRNA encoding H(1) receptor and iNOS by RT-PCR in autoimmune myocarditis with special reference to changes in heart contractility.

Cardiac tissue from autoimmune myocarditis mice was studied to evaluate the expression and biological activity of mRNA encoding H(1) receptor and iNOS. BALB/c inbred mice were immunized with heart protein and sacrificed at 20, 45 and 50 days post immunization. Heart contractility studies and RT-PCR assays were performed. Heart from autoimmune myocarditis mice show mRNA iNOS-related dysfunction with a decrease in heart contractility. This effect was accompanied with an increase production of cyclic GMP and was improved by treating autoimmune mice with an inhibitor of iNOS activity. In addition, autoimmune myocardium expressed an active histamine H(1) receptor mRNA coupled to phospholipase C. The activation of H(1) receptor by ThEA stimulated both phosphoinositide hydrolysis and heart contractility. Normal myocardium did not expressed neither iNOS mRNA nor H(1) receptor mRNA. In conclusions: the development of autoimmune cardiac dysfunction was associated with the expression of iNOS mRNA, cyclic GMP accumulation and the expression of an active histamine H(1) receptor mRNA with increase production of inositol phosphates. These protein emergence during the course of autoimmune myocarditis may be involved a distinct compensatory mechanism operating in this disease.

Animals↗