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PubMed1971

Fine structural localization of acyltransferases. The monoglyceride and -glycerophosphate pathways in intestinal absorptive cells.

A study of the fine structural localization of the acyltransferases of the monoglyceride and alpha-glycerophosphate pathways for triglyceride synthesis in the intestinal absorptive cell is reported. Glutaraldehyde-fixed tissue was found to synthesize diglyceride and triglyceride from monopalmitin and palmityl CoA, and parallel morphological studies showed the appearance of lipid droplets in the smooth endoplasmic reticulum of the absorptive cell. Glutaraldehyde-fixed tissue also synthesized triglyceride from alpha-glycerophosphate, although this enzyme system was more susceptible to fixation than the monoglyceride pathway acyltransferases. Cytochemical methods for the localization of free CoA were based (a) on the formation of the insoluble lanthanium mercaptide of CoA and (b) on the reduction of ferricyanide by CoA to yield ferrocyanide which forms an insoluble precipitate with manganous ions. By these methods the monoglyceride pathway acyltransferases were found to be located mainly on the inner surface of the smooth endoplasmic reticulum. The alpha-glycerophosphate pathway acyltransferases were localized mainly on the rough endoplasmic reticulum. Activity limited to the outer cisternae of the Golgi membranes occurred with both pathways. The possible organization of triglyceride absorption and chylomicron synthesis is discussed in view of these results.

Absorption↗
PubMed1991

Separation of the poly(glycerophosphate) lipoteichoic acids of Enterococcus faecalis Kiel 27738, Enterococcus hirae ATCC 9790 and Leuconostoc mesenteroides DSM 20343 into molecular species by affinity chromatography on concanavalin A.

This study shows for the first time microheterogeneity of 1,3-linked poly(glycerophosphate) lipoteichoic acids. The lipoteichoic acids investigated were those of Enterococcus faecalis Kiel 27738 (I), Enterococcus hirae (Streptococcus faecium) ATCC 9790 (II), and Leuconostoc mesenteroides DMS 20343 (III). Lipoteichoic acids II and III are partially substituted by mono-, di-, tri-, and tetra-alpha-D-glucopyranosyl residues with (1----2) interglycosidic linkages. Lipoteichoic acid I is substituted with alpha-kojibiosyl residues only. Lipoteichoic acids I and III additionally carry D-alanine ester. Lipoteichoic acids were separated on columns of concanavalin-A-Sepharose according to their increasing number of glycosyl substituents per chain. It was evident that all molecular species are usually glycosylated and that alanine ester and glycosyl residues occur on the same chains. The chain lengths of lipoteichoic acid I and II vary between 9-40 glycerophosphate residues, whereas those of lipoteichoic acid III appear to be uniform (33 +/- 2 residues). Molecular species differ in the extent of glycosylation but their content of alanyl residues is fairly constant. All lipoteichoic acids contain a small fraction (5-15%) different in composition from the bulk and most likely reflecting an early stage of biosynthesis. Two procedures for chain length determination of poly(glycerophosphate) lipoteichoic acids are described.

Chromatography, Affinity↗
PubMed1995

Beta-glycerophosphate accelerates calcification in cultured bovine vascular smooth muscle cells.

Calcification is a common feature of advanced atherosclerotic lesions and is being reemphasized as a clinically significant element of vascular disease. However, the scarcity of in vitro models of vascular calcification preclude studying its molecular and cellular mechanism. In the present study, we describe an in vitro calcification in which diffuse calcification can be induced by culturing bovine vascular smooth muscle cells (BVSMC) in the presence of beta-glycerophosphate, ascorbic acid, and insulin in a manner analogous to in vitro mineralization by osteoblasts. Calcification was confirmed by von Kossa staining and 45Ca accumulation. Factor analysis revealed that beta-glycerophosphate is the most important factor for this calcification process, suggesting that alkaline phosphatase (ALP) may be involved. As predicted, high levels of ALP expression were detected by ALP assay and Northern blot analysis. Functional significance of ALP was confirmed by demonstrating that levamisole, a specific inhibitor of ALP, inhibited BVSMC calcification in a dose-dependent manner. Bisphosphonates such as etidronate and pamidronate potently inhibited BVSMC calcification, suggesting that hydroxyapatite formation may be involved. Importantly, expression of osteopontin mRNA was dramatically increased in calcified BVSMC compared with uncalcified control cells. These data suggest that beta-glycerophosphate can induce diffuse calcification by an ALP-dependent mechanism and that this in vitro calcification system is useful for analyzing the molecular and cellular mechanisms of vascular calcification.

Alkaline Phosphatase↗
PubMed1990

L-alpha-glycerophosphate binding to bovine gamma-crystallin: a potential link between metabolism and supramolecular order.

The highly selective nature of protein-ligand interactions provides a sensitive mechanism for the modulation of cellular activity by proteins. In the eye lens the supramolecular order of the lens crystallins, which is expected to be susceptible to protein electrostatic charge, in part defines transparency. The binding of charged ligands to proteins is one way of achieving an alteration in protein electrostatic charge. Evidence is presented that L-alpha-glycerophosphate, a major phosphorus metabolite of eye lens metabolism, binds to the globular protein, gamma-crystallin with moderately high affinity and in a positive cooperative manner. The following binding parameters were obtained from equilibrium measurements: minimum number of binding sites, n = 2; Kassoc = 6.2 +/- 0.5 x 10(3) M-1; cooperativity parameter, alpha H = 1.9 +/- 0.1. Interactive computer graphics display techniques were used to locate putative ligand binding sites, and in turn, to identify the possible molecular interactions responsible for the binding of ligand to protein at one of the sites. One putative binding site was located in the cleft between the two domains of gamma II-crystallin. Arginyl residues 79 and 147 are involved in ligand binding as are the peptide carbonyl oxygens of residues Tyrosyl-50 and Aspartyl-156. Five hydrogen bonds between the ligand and the protein structure are predicted for the binding of L-alpha-glycerophosphate, whereas only 3 occur for the binding of the "unnatural" D-enantiomorph. Modulation of both lens protein supramolecular organization and lens metabolism is predicted to be a consequence of L-alpha-glycerophosphate binding to gamma-crystallin in the lens.

Animals↗
PubMedDate not supplied

[Activity of various enzymes of the initial stages of glycerolipid biosynthesis and glycerophosphate content in alcoholic intoxication].

A distinct increase in activity of glycerokinase and glycerophosphate dehydrogenase and in content of L-alpha-glycerophosphate were observed in brain and liver tissues of rats treated with ethanol for 40 days. The similar alterations were observed after treatment with ehtanol for 80 days but in these conditions the content of L-alpha-glycerophosphate in liver tissue was decreased.

Alcoholic Intoxication↗
PubMed2001

Activation of mitochondrial glycerophosphate cytochrome c reductase in regenerating rat liver by triiodothyronine.

Triiodothyronine administration before partial hepatectomy increased the activity of mitochondrial glycerophosphate cytochrome c reductase. The enzyme activity was further activated after partial hepatectomy during the regenerative process. Our findings showed that: a) the increase of glycerophosphate cytochrome c reductase induced by triiodothyronine was further potentiated by the regeneration process, b) the high activity of the glycerophosphate shuttle was maintained after partial hepatectomy during the period, when most of the liver tissue had again been recovered.

Animals↗
PubMed1979

Reconstruction of rat skeletal muscle glycerophosphate shuttle.

The activity of alpha-glycerophosphate shuttle in homogenate and in a reconstructed system (isolated mitochondria and cytoplasm) from rat skeletal muscle is presented. The influence of some inhibitors of mitochondrial alpha-glycerosphate dehydrogenase on the activity alpha-glycerophosphate shuttle is demonstrated. The possible operativity of alpha-glycerophosphate shuttle in skeletal muscle in vivo is discussed.

Animals↗
PubMed1967

Phosphatidyl glycerophosphate phosphatase.

An enzyme (phosphatidyl glycerophosphate phosphatase) that catalyzes the formation of phosphatidyl glycerol from phosphatidyl glycerophosphate has been rendered soluble by treatment of the particulate fraction of E. coli with Triton X-100 in the presence of EDTA, and has been partially purified. The enzyme is specific for phosphatidyl glycerophosphate and does not catalyze the hydrolysis of other simple phosphomonoesters. It requires Mg(++) for activity and is inhibited by sulfhydryl agents. Some other properties of the enzyme are also described.

Chromatography↗
PubMedDate not supplied

[Impairment of glycerophosphate and glycerol turnover in myocardium under conditions of experimental pancreatitis].

Initial steps of the experimental pancreatitis were characterized by an increase in glycerophosphate accumulation as well as in activity of glycerokinase, glycerophosphate dehydrogenase and glycerol dehydrogenase; content of free glycerol and dihydroacetone phosphate was also increased. Within the subsequent periods the patterns studied exhibited normalization except of glycerokinase and glycerophosphate dehydrogenase activity of which was distinctly decreased as compared with the controls.

Animals↗
PubMed1993

Deficient activity of FAD-linked glycerophosphate dehydrogenase in islets of GK rats.

In pancreatic islet extracts of rats with hereditary non-insulin-dependent diabetes mellitus (GK rats), the activity of the mitochondrial FAD-linked glycerophosphate dehydrogenase, as measured by either a radioisotopic or colorimetric procedure, only represented 30 to 40% of that found in control rats. This decrease in enzymic activity was not attributable to any sizeable change in either islet DNA content or the relative contribution of insulin-producing beta cells to total islet mass. It contrasted with a normal activity of other mitochondrial dehydrogenases and hexokinase isoenzymes. It coincided, however, with an increased activity of glutamate-pyruvate transaminase, as already observed in adult rats injected with streptozotocin during the neonatal period. The decreased activity of islet FAD-linked glycerophosphate dehydrogenase also contrasted with an increased activity of the same enzyme in the liver of GK, as compared to control rats. In the light of these findings and recent metabolic data collected in intact islets of GK rats, it is proposed that a deficiency of beta-cell FAD-linked glycerophosphate dehydrogenase, the key enzyme of the glycerol phosphate shuttle, may represent a cause of inherited non-insulin-dependent diabetes.

Alanine Transaminase↗
PubMed1993

Streptozotocin-induced FAD-glycerophosphate dehydrogenase suppression in pancreatic islets. Relationship with the severity and duration of hyperglycaemia and resistance to insulin or riboflavin treatment.

In vitro, streptozotocin (1.0-2.0 mM) fails to exert any immediate effect on the activity of FAD-glycerophosphate dehydrogenase in either pancreatic islet homogenate or freshly isolated intact islets. However, when injected in vivo, streptozotocin (40 mg/kg body weight) lowers the specific activity of the FAD-linked enzyme in islet homogenates within 24 h, whilst causing little change in 2-ketoglutarate dehydrogenase and increasing glutamate dehydrogenase islet activity. In animals which became frankly hyperglycaemic as the result of the injection of streptozotocin, the activity of islet FAD-glycerophosphate dehydrogenase, measured 2 weeks after administration of the B-cell cytotoxic agent, was decreased to 10-20% of its control value. Neither insulin treatment nor riboflavin supplementation affected this enzymic defect. Even when the animals injected with streptozotocin remained virtually euglycaemic, the activity of islet FAD-glycerophosphate dehydrogenase was markedly decreased. This coincided with a preferential impairment of aerobic glycolysis, as judged from the ratio between D-[3,4-14C]glucose oxidation and D-[5-3H] glucose utilization by the islets. It is proposed, therefore, that the administration of sub-diabetogenic amounts of streptozotocin to adult rats represents an alternative and easier approach to the study of B-cell dysfunction in this model of type 2 (non-insulin-dependent) diabetes than does streptozotocin injection in neonatal rats.

Alloxan↗
PubMed1993

Effect of streptozotocin and nicotinamide upon FAD-glycerophosphate dehydrogenase activity and insulin release in purified pancreatic B-cells.

Purified rat pancreatic insulin-producing B-cells, which display a 12-fold higher activity of FAD-linked glycerophosphate dehydrogenase than other islet endocrine cells, were exposed for 30 min to 2 mM streptozotocin and subsequently cultured for 2 days in the absence or presence of 2 mM nicotinamide. Streptozotocin decreased by 54% the number of B-cells and, in surviving cells, lowered by 75% the activity of FAD-linked glycerophosphate dehydrogenase, whilst failing to affect that of glutamate dehydrogenase. This coincided with a 42-51% reduction of insulin secretion, when expressed relative to either the DNA or hormonal content of surviving cells. After exposure to streptozotocin, the presence of nicotinamide in the culture medium reduced cell death by 44% and also reduced the deleterious effects of streptozotocin upon both the enzymic and secretory activities of surviving cells. These findings indicate that the decreased activity of FAD-linked glycerophosphate dehydrogenase previously documented in pancreatic islets from streptozotocin-injected rats, as well as the protective effect of nicotinamide thereupon, are not attributable solely to changes in the number of B-cells but also to an altered enzymic activity in surviving B-cells. The latter anomaly may account, in part at least, for an impaired B-cell secretory response to D-glucose.

Animals↗
PubMed1994

Impaired FAD-glycerophosphate dehydrogenase activity in islet and liver homogenates of fa/fa rats.

The mitochondrial FAD-linked enzyme glycerophosphate dehydrogenase plays a key role in the pancreatic B-cell glucose sensing device. In the present study, the activity of this enzyme was examined in islets of fa/fa rats in which inherited diabetes mellitus is associated with obesity, hyperinsulinism and severe insulin resistance. The specific activity of both FAD-linked glycerophosphate dehydrogenase and glutamate dehydrogenase were decreased in islet and liver homogenates prepared from fa/fa, as compared to Fa/Fa, rats, this coinciding with a low ratio between glutamateoxalacetate and glutamate-pyruvate transaminase activity in both islet and liver extracts, islet hyperplasia, hyperinsulinemia and hepatic steatosis in the hyperglycemic fa/fa rats. It is speculated that a low activity of FAD-linked glycerophosphate dehydrogenase in the pancreatic B-cell may participate to the perturbation of glucose homeostasis in fa/fa rats, like in other animal models of non-insulin-dependent diabetes mellitus.

Alanine Transaminase↗
PubMed1990

Effects of active immunization against L-triiodothyronine on serum thyrotropin levels and liver mitochondrial alpha-glycerophosphate dehydrogenase activity in rats: evidence for reduced hormone disposal to cells.

Thyroid hormone binding autoantibodies have been observed in serum from patients affected by either thyroid disorders or autoimmune nonthyroid diseases. In most instances, no major involvement of thyroid status of these patients has been reported. However, some authors have attributed the occurrence of hypothyroidism to high capacity thyroid hormone binding autoantibodies. In order to verify such a hypothesis, the effect of these autoantibodies on serum TSH and liver mitochondrial alpha-glycerophosphate dehydrogenase has been investigated in rats, wherein circulating T3-binding antibodies (max cap 10(-12) 10(-8) to mol/l) were induced by active immunization. Starting from the 3rd week after antigen injection, the binding of 125I-T3 to serum immunoglobulins was progressively increased, with a peak at the 5th week. In immunized animals considered as a whole group, serum TSH levels were significantly higher and liver mitochondrial alpha-glycerophosphate dehydrogenase activity was significantly lower than in normal rats (m +/- SE: 145 +/- 15 vs 34 +/- 2 ng/dl and 0.0450 +/- 008 vs 0.0980 +/- 005 delta A. mg/prot/.min, respectively; p less than 0.001). The pattern of both TSH increase and alpha-glycerophosphate dehydrogenase decrease were similar to the evolution of 125-I-T3 binding to serum immunoglobulins, the maximal TSH values and lowest enzyme levels being observed at the 5th week after the beginning of the experiments.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1998

Did archaeal and bacterial cells arise independently from noncellular precursors? A hypothesis stating that the advent of membrane phospholipid with enantiomeric glycerophosphate backbones caused the separation of the two lines of descent.

One of the most remarkable biochemical differences between the members of two domains Archaea and Bacteria is the stereochemistry of the glycerophosphate backbone of phospholipids, which are exclusively opposite. The enzyme responsible to the formation of Archaea-specific glycerophosphate was found to be NAD(P)-linked sn-glycerol-1-phosphate (G-1-P) dehydrogenase and it was first purified from Methanobacterium thermoautotrophicum cells and its gene was cloned. This structure gene named egsA (enantiomeric glycerophosphate synthase) consisted of 1,041 bp and coded the enzyme with 347 amino acid residues. The amino acid sequence deduced from the base sequence of the cloned gene (egsA) did not share any sequence similarity except for NAD-binding region with that of NAD(P)-linked sn-glycerol-3-phosphate (G-3-P) dehydrogenase of Escherichia coli which catalyzes the formation of G-3-P backbone of bacterial phospholipids, while the deduced protein sequence of the enzyme revealed some similarity with bacterial glycerol dehydrogenases. Because G-1-P dehydrogenase and G-3-P dehydrogenase would originate from different ancestor enzymes and it would be almost impossible to interchange stereospecificity of the enzymes, it seems likely that the stereostructure of membrane phospholipids of a cell must be maintained from the time of birth of the first cell. We propose here the hypothesis that Archaea and Bacteria were differentiated by the occurrence of cells enclosed by membranes of phospholipids with G-1-P and G-3-P as a backbone, respectively.

Amino Acid Sequence↗
PubMed2001

Highly efficient Aerococcus viridans L-alpha-glycerophosphate oxidase production in the presence of H2O2-decomposing agent: purification and kinetic characterization.

Glycerophosphate oxidase was purified from Aerococcus viridans cells by phase partitioning in Triton X-114, ammonium sulfate fractionation, FPLC ion-exchange chromatography and FPLC hydrophobic-interaction chromatography. The purification achieved from a crude extract of A. viridans was 38-fold with a 32% recovery of activity. Under the growth conditions used, A. viridans strain CECT 978 proved to be an excellent glycerophosphate-oxidase producer, with enzyme production 2,800-fold greater than that described in the literature for the same microorganism. The culture medium used in the present work is that commonly used for cultivation of this microorganism, except that an H2O2-decomposing enzyme was added. The addition of catalase to the growth medium had a clear effect on the growth rate. Furthermore, methylglyoxal, a metabolite that is formed enzymatically from triose phosphates, was found to be an inactivator of glycerophosphate oxidase activity.

Catalase↗
PubMed1982

Localization of glycerophosphate acyltransferase in Escherichia coli.

sn-Glycero-3-phosphate acyltransferase (EC 2.3.1.15) the first enzyme involved in phospholipid biosynthesis, is known to be associated with the cytoplasmic membrane of Escherichia coli. The localization of this enzyme in the transverse plane of the membrane was investigated by proteolysis of intact and lysed spheroplasts and by inhibition of glycerol 3-phosphate transport into intact cells in the presence of azide. Glycerophosphate acyltransferase was found to be resistant to proteolysis by trypsin in intact spheroplasts, whereas its enzymatic activity could be destroyed completely by trypsin in lysed spheroplasts. These results are in line with a localization of the acyltransferase at the inner aspect of the cytoplasmic membrane. Sodium azide was shown to have no inhibitory effect on glycerophosphate acyltransferase activity. Lack of incorporation of glycero phosphate into the phospholipids of glycerol phosphate transport-negative cells and inhibition of this incorporation in wild-type and glycerol 3-phosphate transport-constitutive cells by azide support a cytoplasmic-oriented localization of the glycerophosphate acyltransferase.

Acyltransferases↗