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PubMed1992

Coenzyme Q-pool function in glycerol-3-phosphate oxidation in hamster brown adipose tissue mitochondria.

We have investigated the role of the Coenzyme Q pool in glycerol-3-phosphate oxidation in hamster brown adipose tissue mitochondria. Antimycin A and myxothiazol inhibit glycerol-3-phosphate cytochrome c oxidoreductase in a sigmoidal fashion, indicating that CoQ behaves as a homogeneous pool between glycerol-3-phosphate dehydrogenase and complex III. The inhibition of ubiquinol cytochrome c reductase is linear at low concentrations of both inhibitors, indicating that sigmoidicity of antimycin A and myxothiazol inhibition is not a direct property of antimycin A and myxothiazol binding. Glycerol-3-phosphate cytochrome c oxidoreductase is strongly stimulated by added CoQ3, indicating that endogenous CoQ is not saturating. Application of the pool equation for nonsaturating ubiquinone allows calculation of the Km for endogenous CoQ of glycerol-3-phosphate dehydrogenase of 3.14 mM. The results of this investigations reveal that CoQ behaves as a homogeneous pool between glycerol-3-phosphate dehydrogenase and complex III in brown adipose tissue mitochondria; moreover, its concentration is far below saturation for maximal electron transfer activity in comparison with other branches of the respiratory chain connected with the CoQ pool. HPLC analysis revealed a lower amount of CoQ in brown adipose mitochondria (0.752 nmol/mg protein) in comparison with mitochondria from other tissues and the presence of both CoQ9 and CoQ10.

Adipose Tissue, Brown↗
PubMed1992

Regulation of mitochondrial glycerol-phosphate dehydrogenase by Ca2+ within electropermeabilized insulin-secreting cells (INS-1).

(1) A new insulin-secreting cell line (INS-1; Asfari et al. (1992) Endocrinology 130, 167-178) has been used to study the regulation by Ca2+ of mitochondrial FAD-linked glycerol-phosphate dehydrogenase (FAD-GPDH) in situ. (2) Enzyme activity was examined on-line in electropermeabilized cells by a new, sensitive, assay. This involved the reduction of the artificial electron acceptor, 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT), monitored by the quenching of the fluorescence of rhodamine-18. Using this approach, similar total levels of FAD-GPDH activity (nmol/min per 10(6) cells) were measured in INS-1 cells (1.35 +/- 0.22) and isolated rat islet cells (1.63 +/- 0.02) (3) Ca2+ ions markedly activated the enzyme, lowering the apparent Km-value for added DL-glycerophosphate from 8.8 +/- 1.4 mM to 1.0 +/- 0.1 mM. Ca2+ had no effect on the apparent Vmax. The enzyme displayed cooperative kinetics with respect to DL-glycerophosphate (Hill coefficient of 2.0 +/- 0.2 and 1.6 +/- 0.2 in the absence and presence respectively of Ca2+). Half-maximal effects of Ca2+ were observed in the range 30-130 nM, depending on the concentration of glycerol phosphate. (4) Enzyme activity was weakly (30%) inhibited by diazoxide, but not by the diabetogenic drug, streptozotocin. (5) The data indicate that INS-1 cells represent an excellent model for studying the rôle of FAD-GPDH in the control of insulin secretion.

Animals↗
PubMed1995

Arsenite release on enzymic transformation of arsonomethyl substrate analogues: a potentially lethal synthesis by glycerol-3-phosphate dehydrogenase.

The isosteric arsenical analogue of glycerol 3-phosphate, 3,4-dihydroxybutylarsonic acid, is a good substrate for rabbit muscle glycerol-3-phosphate dehydrogenase. Its oxidation is accompanied by release of arsenite. This release seems to be due to a spontaneous elimination of arsenite by 3-oxoalkylarsonic acids, as it is also observed in (1) the oxidation of 3-hydroxypropylarsonic acid by yeast alcohol dehydrogenase, (2) treatment of 3,4-dihydroxybutylarsonic acid with periodate and (3) nonenzymic transamination of the glutamate analogue 2-amino-4-arsonobutyric acid. Enzymic formation of 3-oxoalkylarsonic acids in cells can therefore be lethal, as arsenite is poisonous to most organisms because of its high affinity for dithiols such as dihydrolipoyl groups.

Alcohol Dehydrogenase↗
PubMed1985

Dynamic exercise training in foxhounds. II. Analysis of skeletal muscle.

The purpose of this study was to determine whether 8-12 wk of endurance training produces biochemical and histochemical adaptations in skeletal muscle in foxhounds. Analyses were performed on samples removed from gastrocnemius, triceps, and semitendinosus muscles of foxhounds before and after a treadmill running program. Biochemical analysis showed that training did not alter the activities of phosphofructokinase, beta-hydroxyacyl-CoA dehydrogenase, succinate dehydrogenase, or total phosphorylase. Histochemical analysis of myofibrillar actomyosin ATPase demonstrated three distinct classes of type II fibers and one type I fiber in the semitendinosus and triceps muscles and two type II and two type I fibers in the gastrocnemius muscle. Fiber type distribution and oxidative and glycolytic potentials, as indicated by nicotinamide adenine dinucleotide tetrazolium reductase or alpha-glycerophosphate dehydrogenase staining intensity, were unaltered by training. Similarly, capillary density, capillary-to-fiber ratios, and capillary area-to-fiber area ratios did not change with training. Thus, unlike humans and other mammals (i.e., rat), these foxhounds did not manifest biochemical or histochemical adaptations in skeletal muscle as the result of endurance training. This is consistent with the results of the study in which endurance training produced a 27% increase in maximal cardiac output and a 4% increase in maximal arteriovenous O2 extraction in foxhounds.

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed1992

Histoenzymological demonstration of glycerol-3-phosphate dehydrogenase and succinate dehydrogenase in the telencephalic nuclei and fibre tracts of hillstream cyprinoid, Barilius bendelisis (Hamilton).

The authors studied the regional localization of two dehydrogenases--glycerol-3-phosphate dehydrogenase and succinate dehydrogenase--in the telencephalic nuclei and fibre tracts of Barilius bendelisis by histoenzymological methods. The activity of these dehydrogenases varied from moderately positive to strongly positive in the nuclear areas and from intensely to strongly positive in the fibre tracts, except those related to the olfactory tubercle. G3PD appears to play an important role in the biosyntheses of phospholipids and to form a link between glycolysis and the pathway of the hexose-monophosphate shunt, in addition to its usual role in the degradation of glucose, along with other dehydrogenases, including succinate dehydrogenase.

Animals↗
PubMed1986

Glyburide action in cultured 3T3-L1 adipocytes.

During adipocyte differentiation of 3T3-L1 cells, glyburide increased the specific activity (mU/mg protein) of glycerol-3-P dehydrogenase (by at least 14-fold) and glutamine synthetase (by 5-fold). The glyburide-mediated increases in enzyme activities were greater in the presence than in the absence of insulin. Our data indicate that glyburide either potentiates or mimics the actions of insulin to increase the activity of glycerol-3-P dehydrogenase during adipocyte differentiation of cultured 3T3-L1 cells.

Adipose Tissue↗