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A soluble l-alpha-glycerophosphate dehydrogenase, which is stimulated by FAD and is independent of added pyridine nucleotides, functions during anaerobic catabolism of glycerol and l-alpha-glycerophosphate by Escherichia coli.
The electrophoretic characteristics of the hepatic mitochondrial cytochrome-linked alpha-glycerophosphate dehydrogenase (CGPD) induced by thyroid hormone have been examined. Mitochondria, derived from livers of C57BL/6J or BALB/cAnN mice after 3 days of L-3,5,3'-triiodothyronine (T3) (0.1 mumole) or saline administration, were extracted with Triton X-100 (5 ml/l), and the extracts subjected to alkaline discontinuous polyacrylamide gel electrophoresis. The enzyme was located on the gel by means of a histochemical stain. The migration of CGPD from T3-treated mice was identical with that from saline-treated mice in both strains, and differed from that of NAD-linked alpha-glycerophosphate dehydrogenase. This suggests that the induction does not involve the activation of a new gene for a CGPD isoenzyme that is not expressed in the basal state. In addition, enzyme from both strains of mice exhibited identical rates of migration, indicating that the enzymes from both strains are chemically identical. These conclusions must be considered tentative, pending other studies to disprove the presence of new molecular species with no change in net charge or size.
In rats that received a low protein isocaloric diet (protein content of the diet: 8 instead of 20%) during fetal life and thereafter up to the time of sacrifice at 12-13 weeks of age, a low plasma insulin concentration, a decreased insulin content of isolated pancreatic islets, and an impaired secretory response of the islets to either D-glucose or the association of L-leucine and L-glutamine coincided, in islet homogenates, with a low activity of the mitochondrial glycerophosphate dehydrogenase and an abnormally high ratio between glutamate-alanine and glutamate-aspartate transaminase activities. Opposite enzymatic changes were found in liver extracts of the same rats. No obvious change in these hormonal, secretory, and enzymatic variables were observed when the period of protein deficiency was restricted to fetal life. These findings support the view that, in protein malnutrition, an impaired activity of pancreatic B-cell mitochondrial glycerophosphate dehydrogenase contributes, possibly in association with other enzymatic anomalies, to the perturbation of islet function.
alpha-glycerophosphate dehydrogenase (alpha-GPDH-EC.1.1.1.8) has been considered absent in Trypanosoma cruzi in contradiction with all other studied trypanosomatids. After observing that the sole malate dehydrogenase can not maintain the intraglycosomal redox balance, GPDH activity was looked for and found, although in very variable levels, in epimastigotes extracts. GPDH was shown to be exclusively located in the glycosome of T. cruzi by digitonin treatment and isopycnic centrifugation. Antibody against T. brucei GPDH showed that this enzyme seemed to be present in an essentially inactive form at the beginning of the epimastigotes growth. GPDH is apparently linked to a salicylhydroxmic-sensitive glycerophosphate reoxidizing system and plays an essential role in the glycosome redox balance.
Two genes that have potentially important regulatory roles in insulin secretion are both located on chromosome 2q24.1. G-protein-coupled muscarinic potassium channel (GIRK1) is an inwardly rectifying K+ channel that helps to maintain the resting potential and excitability of cells. Mitochondrial FAD-linked glycerophosphate dehydrogenase (m-GDH) catalyzes a rate-limiting step of the glycerol phosphate shuttle in pancreatic islets. Reduced m-GDH activity has been demonstrated in islets isolated from diabetic subjects compared with islets from nondiabetic control subjects and from the diabetic GK rat. To study the relationship between these candidate genes and NIDDM, we have examined a simple tandem-repeat polymorphism (STRP) close to both the KCN J3 (GIRK1) locus and the m-GDH locus. In a linkage study of three maturity-onset diabetes of the young (MODY) pedigrees, not linked to MODY1, MODY2, or MODY3, a cumulative score of - 9.6 at a recombination fraction of theta = 0 excluded linkage. In a population-association study, no linkage disequilibrium for the STRP was found between 190 unselected NIDDM patients and 60 geographically and age-matched white nondiabetic subjects (chi2 = 1.51 on 3 df, P = 0.68). Thus, mutations involving the genes for GIRK1 or FAD-glycerophosphate dehydrogenase are unlikely to cause MODY, and a common mutation in either gene is unlikely to contribute to NIDDM in whites. These data do not exclude mutations in some families or other ethnic groups.
Reducing equivalents for the electron transport chain are generated within the mitochondria by the Krebs cycle and in cytoplasm by processes like lipid metabolism. Two mitochondrial enzymes, succinate dehydrogenase (SDH), a prominent enzyme in the Krebs cycle, and alpha-glycerophosphate dehydrogenase (alpha-GPDH), half of the glycerophosphate shuttle system for bringing reducing equivalents from cytoplasm to mitochondria, were examined enzyme histochemically to assess the contribution of each to metabolism of the developing canine retina. SDH activity, a common marker for oxidative metabolism, was insignificant at birth. By 4 days of age, activity was observed only in developing photoreceptor inner segments. By 21 days of age SDH activity was present throughout the retina, especially in photoreceptor inner segments and plexiform layers, and approached the level observed in the adult dog. Menadione-linked alpha-GPDH (M-alpha-GPDH) activity, however, was prominent in developing vasculature and outermost portion of the neuroblastic layer of the 1 day-old retina. Most notable was localization in vascular precursors, angioblasts, found distant from formed vessels in the peripheral nerve fiber layer. Retinal dependence on an oxidative metabolism in neuronal elements, as represented by SDH activity, occurs only when the vasculature is well established.
An acquired or inherited deficiency of FAD-linked glycerophosphate dehydrogenase activity in the pancreatic islet B-cell was recently proposed to represent a far-from-uncommon contributing factor in the pathogenesis of non-insulin-dependent diabetes mellitus. In the present study, it was investigated whether the postulated genomic defect coincides with the biosynthesis of an enzymic protein with altered catalytic properties and might concern an isoenzyme distinct from that found in extrapancreatic tissues. The activity of FAD-linked glycerophosphate dehydrogenase, as measured by either a radioisotopic or colorimetric procedure, was indeed severely decreased in islets from rats injected with streptozotocin. The intrinsic properties of the enzyme were preserved, however, as judged from the affinity for L-glycerol-3-phosphate, the ratio in reaction velocity using either FAD or iodonitrotetrazolium as electron acceptor and the activation of the enzyme by Ca2+. When the same kinetic parameters were compared in islet, liver and spleen homogenates from normal rats, significant differences were observed, however, between these three tissues, suggesting the possible existence of distinct isoenzymes.
Preadipocyte subclones derived from mouse 3T3 cells differentiate into adipocytes; this differentiation is characterized by an increased activity of numerous enzymes required for triglyceride synthesis and/or mobilization. Among these enzymes, the role of glycerophosphate dehydrogenase in the differentiation process has been previously reported. In the present work, we studied the hormonal regulation of glycerophosphate dehydrogenase gene expression (G3PDH) in differentiated 3T3-F442A adipocytes. Dexamethasone (DEX) elicited a 50% decrease in both mRNA content and specific activity of G3PDH. This effect was due to a posttranscriptional event since DEX shortened the half life of the mRNA, whereas it did not modify the transcription rate of this gene. The DEX effect is specific to G3PDH, since the expression of another adipose-specific gene, namely adipsin, is not modified by DEX treatment. Insulin counteracts the inhibitory effect of DEX, mainly by stabilizing the mRNA encoding for G3PDH. The antiglucocorticoid RU38486 is able to reverse DEX inhibition. Latter phenomenon suggests that DEX action on G3PDH gene expression could be mediated by glucocorticoid receptors.
A rapid three-step procedure is presented for the purification of flavin-linked L-3-glycerophosphate dehydrogenase (E.C. 1.1.99.5.) from rat liver mitochondria. Solubilization of the enzyme is achieved selectively by digitonin, at a detergent-to-protein ratio of 0.7 mg/mg (mitochondrial protein concentration 10 mg/ml). The procedure involves chromatography on hydroxymethyl-hexamethylenediamine-succinyl-hexamethylenediamin e Sepharose 4B, followed by anion exchange chromatography using a FPLC technique. Subunit molecular weight of the enzyme was found to be 77,000 when prepared in the presence of the protease inhibitor phenylmethylsulphonyl fluoride. The Kmapp value for glycerophosphate was not influenced by the purification, and the ability of the enzyme to be activated by Ca2+ was preserved as well.
alpha-Glycerophosphate dehydrogenase (EC 1.1.99.5) in mitochondria from liver of the triiodothyronine-treated rats is competitively inhibited by phosphoenolpyruvate, glyceraldehyde 3-phosphate and 3-phosphoglycerate, the apparent Ki values for phosphoenolpyruvate being 0.76 mM at pH 7.0, 1.7 mM at pH 7.4 and 3.5 mM at pH 7.7. The apparent Ki values for glyceraldehyde 3-phosphate and 3-phosphoglycerate are also pH-dependent. Other glycolytic intermediates, such as 2-phosphoglycerate, 2,3-diphosphoglycerate, pyruvate, glucose 6-phosphate, fructose 6-phosphate and fructose 1,6-diphosphate did not alter significantly alpha-glycerophosphate dehydrogenase activity. Palmitoyl-CoA is a competitive inhibitor of this enzyme, with Ki value of about 30 micron.
Specific L-3,3'5-triiodothyronine (triiodothyronine) binding by isolated nuclei was determined in N-nitrosomethylurea-induced mammary carcinomas and livers from intact and thyroidectomized animals. Tumors contained a single class of high-affinity nuclear triiodothyronine binding sites with characteristics similar to those of hepatic nuclei. Competition experiments showed the relative affinities of thyroid hormone structural analogues for both tumor and liver receptors to be: triiodothyroacetic acid greater than triiodothyronine greater than thyroxine greater than reverse triiodothyronine. Diiodotyrosine did not complete for the binding sites. Mammary tumors exhibited a wide range of binding sites, but most were in the range of 50 to 150 fmol/micrograms DNA. The levels were not affected significantly by hypothyroidism. Liver triiodothyronine receptor concentrations were approximately 5-fold those of tumors; they were unaffected by low serum thyroid hormone levels and were similar to those of non-tumor-bearing, euthyroid controls. Mitochondrial alpha-glycerophosphate dehydrogenase and cytosolic malic enzyme activities were reduced in both tumors and livers of hypothyroid rats; cytosolic alpha-glycerophosphate dehydrogenase levels were unchanged. Hepatic enzyme activities were similar in euthyroid tumor-bearing animals and in euthyroid healthy controls.
Hepatocytes isolated from normal adult rats were cultured under serum-free conditions. Induction of mitochondrial alpha-glycerophosphate dehydrogenase (glycerol 3-phosphate dehydrogenase) (EC 1.1.99.5; sn-glycerol-3-phosphate: (acceptor) oxidoreductase) and cytosolic malic enzyme (EC 1.1.1.40; L-malate-NADP+ oxidoreductase (decarboxylating)) by 3,3'-5-triiodo-L-thyronine (triiodothyronine) in the culture medium follows the same time course as the in vivo response to thyroid hormones. The addition of 1 microM cycloheximide blocks the triiodothyronine response. Thyroxine is also capable of stimulating the activities of both enzymes. Although increases in alpha-glycerophosphate dehydrogenase and malic enzyme activities are observed when triiodothyronine is added to the culture medium for 3 days (62% and 36%, respectively), in the presence of insulin and cortisol the response is significantly greater. Dexamethasone is more potent than cortisol in increasing triiodothyronine action. In the presence of bovine serum albumin, to prevent metabolism of triiodothyronine, hepatocytes show increased enzyme activity at concentrations as low as 10(-10) M triiodothyronine.
Hexokinase, aldolase, L-alpha-glycerophosphate dehydrogenase, and lactate dehydrogenase activities were determined in the kidney of the aging cat. Kidneys from 24 domestic cats 2 months to 7.5 years old in 6 age groups were examined by light microscopic and histochemical methods. Enzyme activities in anatomic components of the kidney were assessed on a quantitative basis for evaluation of mean activity between the age groups. In the cats with advancing age, renal components generally had stable activity. A significant (P less than 0.05) increase in hexokinase activity occurred with advancing age in the ascending part of the renal loop (Henle's loop) and in the distal convoluted tubule. Significant (P less than 0.05) increases in aldolase activity with aging were in cortical connective tissue, internal part of the glomerular capsule (podocytes), distal convoluted tubule, and convoluted segment (Pi) of the proximal portion of the nephron tubule. L-alpha-glycerophosphate dehydrogenase and lactate dehydrogenase activity increased significantly with aging in the convoluted (Pi) segment of the proximal portion of the nephron tubule.
Growing surface cultures of 3T3 cells possess a low level of glycerophosphate dehydrogenase, an important enzyme in triglyceride synthesis. When 3T3-C2, a subline that does not undergo appreciable adipose conversion, reaches confluence, the level of the enzyme does not increase. In 3T3-F442A, a subline that undergoes the conversion with high frequency, the specific activity of the enzyme increases about 600-fold. The enzyme of the adipose 3T3 cells is different from that of non-adipose 3T3 cells in its thermal stability and its affinity for dihydroxyacetone phosphate. The enzyme of the adipose cells probably corresponds to the stable "adult" form of the enzyme, as described previously, and the enzyme of non-adipose 3T3 cells is probably the unstable "embryonic" form. For this reason, the change in the enzyme that takes place during the adipose conversion is greater than would be indicated simply by the total increase in specific activity. If, as seems likely, the two forms of glycerophosphate dehydrogenase are the products of independent genes, the adipose conversion may activate a hitherto silent gene for the stable enzyme.
The esterases, leucine aminopeptidase and alpha-glycerophosphate dehydrogenase revealed modifications in gene expressions during the development of Anopheles darlingi. The esterases showed five activity bands, 1 and 2 being more deeply stained during the larval stages than in pupae or adults, esterases 3 and 4 more deeply stained in pupae and adults whereas esterase 5 was present throughout development. Leucine aminopeptidase showed five activity bands: LAP2 and LAP5 were characteristic of larvae, LAP3 was specific for pupae and adults, LAP4 was detected only in pupae, and LAP1 and LAP6 were detected in all stages. alpha-Glycerophosphate dehydrogenase presented one activity band on starch gel whose intensity increased with development. Two activity bands were detected on polyacrylamide gel (alpha-GPDH1 and alpha-GPDH2) in 4th-instar larvae (old pigmented larvae) and this activity increased with development.
When fetal rat calvarial cells are cultured in medium containing vitamin C, osteoid nodules develop after approximately 15 days of culture. Upon addition of an organic phosphate (beta-glycerophosphate, beta GP), these nodules mineralize. We have now used this system to explore the suggestion made by others that a negative feedback may exist between matrix mineralization on the one hand and the synthesis of alkaline phosphatase and bone matrix collagen on the other by analyzing the synthesis of these proteins and the levels of their mRNAs in mineralizing and nonmineralizing cultures. Our results indicate that in the osteoid nodule-bone nodule system, matrix mineralization did not affect the mRNA levels for osteopontin, type I collagen, bone sialoprotein, or osteocalcin. Synthesis of total protein and collagen and the osteocalcin content of culture media were also not different in the mineralizing and nonmineralizing cultures. However, alkaline phosphatase mRNA was increased in early mineralizing cultures and alkaline phosphatase activity in the cell layer was also increased in mineralizing cultures. Thus, the hypothesis that a direct negative feedback exists between mineralization and matrix protein synthesis is not supported by our experiments.
Differentiating chick limb-bud mesenchymal cells plated in micromass culture form a cartilage matrix that can be mineralized in the presence of 4 mM inorganic phosphate (Pi), and 1 mM calcium. Previous studies showed that when beta-glycerophosphate (beta GP) is used in place of Pi, the mineral crystals formed are larger and differ in distribution. The present study shows that the difference in distribution is not associated with alterations in cell proliferation, protein synthesis, or with collagen, proteoglycan core protein, or alkaline phosphatase gene expression. Cultures with 2.5, 5, and 10 mM beta GP did show different levels of alkaline phosphatase activity, and in the presence of low (0.3 mM) Ca had different Pi contents (4, 6 and 9 mM, respectively), indicating that the increase in CaxP product may in part be responsible for the altered pattern of mineralization. However, cultures with beta GP in which alkaline phosphatase activity was inhibited with levamisole still had an altered mineral distribution as revealed by Fourier transform-infrared (FT-IR) microspectroscopy. The presence of a casein kinase II-like activity in the mineralizing cultures, the ability of specific inhibitors of this enzyme to block mineralization, and the known ability of beta GP to block phosphoprotein phosphatase activity suggests that altered patterns of matrix protein phosphorylation may influence mineral deposition in these cultures.
Mineralization occurred both in fetal rat calvarial cells and UMR 106 osteoblastic cells when they were cultured in medium containing L-ascorbate and beta-glycerophosphate as evidenced by von Kóssa staining as well as deposition of calcium ions and inorganic phosphate in the cells. When compared with corresponding non-mineralized cell cultures, both the mineralized cultures of calvarial cells and UMR 106 cells did not exhibit any change in intracellular bone-specific alkaline phosphatase activities which were measured by wheatgerm lectin precipitation method. Our results support the hypothesis that mineralization may not exert any direct negative feedback on matrix protein synthesis in osteoblasts during bone formation.