Biomedical subjects

A M Loiseau

Publications and source records attributed to A M Loiseau.

4 recordsLinked to original sources

PubMed1991

The cytosolic and glycosomal glyceraldehyde-3-phosphate dehydrogenase from Trypanosoma brucei. Kinetic properties and comparison with homologous enzymes.

The protozoan haemoflagellate Trypanosoma brucei has two NAD-dependent glyceraldehyde-3-phosphate dehydrogenase isoenzymes, each with a different localization within the cell. One isoenzyme is found in the cytosol, as in other eukaryotes, while the other is found in the glycosome, a microbody-like organelle that fulfils an essential role in glycolysis. The kinetic properties of the purified glycosomal and cytosolic isoenzymes were compared with homologous enzymes from other organisms. Both trypanosome enzymes had pH/activity profiles similar to that of other glyceraldehyde-3-phosphate dehydrogenases, with optimal activity around pH 8.5-9. Only the yeast enzyme showed its maximal activity at a lower pH. The glycosomal enzyme was more sensitive to changes in ionic strength below 0.1 M, while the cytosolic enzyme resembled more the enzymes from rabbit muscle, human erythrocytes and yeast. The affinity for NAD of the glycosomal enzyme was 5-10-fold lower than that of the cytosolic, as well as the other enzymes. A similar, but less pronounced, difference was found for its affinity for NADH. These differences are explained by a number of amino acid substitutions in the NAD-binding domain of the glycosomal isoenzyme. In addition, the effects of suramin, gossypol, agaricic acid and pentalenolactone on the trypanosome enzymes were studied. The trypanocidal drug suramin inhibited both enzymes, but in a different manner. Inhibition of the cytosolic enzyme was competitive with NAD, while in the case of the glycosomal isoenzyme, with NAD as substrate, the drug had an effect both on Km and Vmax. The most potent inhibitor was pentalenolactone, which at micromolar concentrations inhibited the glycosomal enzyme and the enzymes from yeast and Bacillus stearothermophilus in a reversible manner, while the rabbit muscle enzyme was irreversibly inhibited.

Animals↗

PubMed1988

Rat hepatoma (HTC) cell 6-phosphofructo-2-kinase differs from that in liver and can be separated from fructose-2,6-bisphosphatase.

6-Phosphofructo-2-kinase was purified from rat liver and hepatoma (HTC) cells. The HTC cell enzyme had kinetic properties different from those of the liver enzyme (more sensitive to inhibition by citrate and not inhibited by sn-glycerol 3-phosphate) and was not a substrate of the cyclic-AMP-dependent protein kinase. Unlike the liver enzyme, which is bifunctional and phosphorylated by fructose 2,6-[2-32P]bisphosphate, the HTC cell enzyme contained no detectable fructose-2,6-bisphosphatase activity and phosphorylation by fructose 2,6-[2-32P]-bisphosphate could not be detected. HTC cell fructose-2,6-bisphosphatase could be separated from 6-phosphofructo-2-kinase activity by purification. Antibodies raised against liver 6-phosphofructo-2-kinase did not precipitate HTC cell fructose-2,6-bisphosphatase whose kinetic properties were completely different from those of the liver enzyme.

Animals↗

PubMed1985

Fructose 2,6-bisphosphate and the control of glycolysis by glucocorticoids and by other agents in rat hepatoma cells.

The rate, key enzymes, and several metabolites of glycolysis in rat hepatoma (HTC) cells have been compared to those in rat hepatocytes. At 5 to 10 mM glucose, lactate release was greater in HTC cells. This could be explained in part by the absence of key gluconeogenic enzymes, by the substitution of glucokinase by hexokinase, and by an increase in phosphofructokinase 1 and pyruvate kinase activity. In addition, fructose 2,6-bisphosphate, the most potent stimulator of phosphofructokinase 1, was identified in HTC cells and shown to stimulate phosphofructokinase 1 partially purified from these cells. Dexamethasone increased the release of lactate in HTC cells. This glucocorticoid increased the concentration of fructose 2,6-bisphosphate and the Vmax of the enzyme that catalyzes its synthesis, phosphofructokinase 2. The data were consistent with an indirect effect at the gene level, mediated by glucocorticoid receptors. Dexamethasone had no effect on the other rate-limiting glycolytic enzymes. Several agents (adenosine, dibutyryl cyclic adenosine 3':5'-monophosphate, ethanol, antimycin) known to decrease fructose 2,6-bisphosphate in hepatocytes were without effect on this stimulator in HTC cells. DL-Glyceraldehyde inhibited glycolysis in HTC cells and eventually killed them. Although this substance decreased fructose 2,6-bisphosphate inhibition of glycolysis through an action at another level could not be ruled out.

Adenosine↗

PubMed1981

Platelet-activating factor acether (PAF-acether) involvement in acute inflammatory and pain processes.

PAF-acether is a potent aggregating agent released by various cells involved in acute inflammatory process. In this paper, exogenous PAF-acether has been investigated for its ability to generate signs of inflammation (edema measured by plethysmometry) and hyperalgesia (Randall-Sellito test) by standard subplantar injection in the rat paw. From 0.005 microgram. PAF-acether induced significant edema of the paw, maximal 1 hour after injection; it was dose-dependent from 0.1 to 5 microgram. Significant dose-dependent hyperalgesia occurred from 1.25 microgram; it reached a plateau from 2 to 4 hours after injection. Both phenomena were long-lasting (greater than 6 h). PAF-acether was 1.5 to 10 times stronger than PGI2 and PGE2 in inducing edema, pain, and in increasing vascular permeability. We investigated the interaction of miscellaneous drugs with the edema and the hyperalgesia caused by 2.5 microgram of PAF-acether. Non-steroidal anti-inflammatory (NSAI) drugs exerted only moderate effects on the edema without affecting hyperalgesia. Edema was highly reduced by various agents: prednisolone, L-cysteine, anti-calcic drugs, theophylline, PGI2, salbutamol, clonidine. All of them, except clonidine, and in contrast to NSAI drugs, were more potent on PAF-acether edema than on kaolin edema; a possible link between these agents is their ability to increase cyclic AMP levels in the cells and consequently to reduce lysosomal enzyme release. PAF-acether itself, injected intra-peritoneally, inhibited PAF-acether edema without preventing pain, at doses inactive on arterial pressure and hematocrit, but inducing marked gastric mucosal damage. Among the drugs tested, including analgesics, only PGI2 and imidazole improved PAF-induced hyperalgesia, showing a dissociation between edema and hyperalgesia not only in their induction (doses of PAF required, time course of the phenomena), but in the drugs able to antagonize their development too.

Analgesics↗