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At least 19 recordsLinked to original sources

PubMed1975

Mutants of Escherichia coli defective in membrane phospholipid synthesis. Phenotypic suppression of sn-glycerol-3-phosphate acyltransferase Km mutants by loss of feedback inhibition of the biosynthetic sn-glycerol-3-phosphate dehydrogenase.

Revertants of Escherichia coli mutants defective in the first enzyme of membrane phospholipid synthesis, sn-glycerol-3-phosphate (glycerol-P) acyltransferase, were investigated. These glycerol-P acyltransferase mutants, selected as glycerol-P auxotrophs, contained membranous glycerol-P acyltransferase activity with an apparent Km for glycerol-P 10 times higher than the parental activity. The glycerol-P acyltransferase activity was also more thermolabile in vitro than the parental activity. Most revertants no longer requiring glycerol-P for growth regained glycerol-P acyltransferase activity of normal thermolability and apparent Km for glycerol-P. However, two novel revertants were isolated which retained an abnormal glycerol-P acyltransferase activity. The glycerol-P dehydrogenase activities of these novel revertants were about 20-fold less sensitive to feedback inhibition by glycerol-P. The feedback-resistant glycerol-P dehydrogenase co-transduced with gpsA, the structural gene for the glycerol-P dehydrogenase. Further transduction experiments demonstrated that the feedback resistant glycerol-P dehydrogenase phenotypically suppressed the glycerol-P acyltransferase Km lesion. The existence of the class of glycerol-P auxotrophs which owe their phenotype to the glycerol-P acyltransferase Km lesion therefore depends on the feedback regulation of glycerol-P synthesis in E. coli.

Acyltransferases↗

PubMed1978

Biosynthesis in Escherichia coli of sn-glycerol 3-phosphate, a precursor of phospholipid. Kinetic characterization of wild type and feedback-resistant forms of the biosynthetic sn-glycerol-3-phosphate dehydrogenase.

Homogeneous wild type and feedback-resistant forms of the biosynthetic sn-glycerol 3-phosphate (glycerol-P) dehydrogenase of Escherichia coli (EC1.1.1.8) were subjected to two-substrate kinetic analysis. The kinetics of the NADPH-dependent reduction of dihydroxyacetone phosphate (dihydroxyacetone-P) and of the NADP-dependent oxidation of glycerol-P indicate that these reactions proceed by a sequential mechanism. Glycerol-P was a competitive inhibitor with respect to dihydroxyacetone-P for both enzymes. The wild type and feedback-resistant glycerol-P dehydrogenases had Ki values for glycerol-P of 4.4 micrometer and 43 micrometer, respectively. Therefore, the sensitivity of the wild type activity and reduced sensitivity of the feedback-resistant activity, both noted previously in crude extracts, were inherent properties of the enzymes. The patterns of product inhibition for both enzymes were identical, and the difference in the inhibition constants for glycerol-P occurred without significant alteration of any other kinetic constant determined. Kinetic mechanisms consistent with the patterns of product inhibition violated Haldane relationships and other kinetic relationships. These discrepancies suggest that glycerol-P inhibition occurs at a site distinct from the active site. The pH dependencies of the Km for dihydroxyacetone-P and the Ki for glycerol-P were markedly different suggesting the existence of an allosteric site. The addition of glycerol-P in the presence of NADPH stabilized both enzymes against thermal inactivation. Half-maximal stabilization was provided by 5 micrometer and 50 micrometer glycerol-P for the wild type and feedback-resistant enzymes, respectively. These kinetic data, considered in conjunction with previous physiologic and genetic data, indicate that the synthesis of glycerol-P is regulated in vivo by glycerol-P inhibition of the glycerol-P dehydrogenase. The data suggest that glycerol-P inhibition occurs at an allosteric, regulatory site.

Dihydroxyacetone Phosphate↗

PubMed1976

Effects of glycerol and glucose on the kinetics of glycerol utilization by adipose tissue in the rat.

To study the kinetics of glycerol utilization by adipose tissue in vitro as function of the concentrations of both glycerol and glucose in the incubation media, pieces of epididymal fat pad from fed rats were incubated for different times in Krebs Ringer bicarbonate supplemented with 1-14C-glycerol and purified albumin. An increase in the concentration of glycerol in the medium produces a decrease in the formation of 14CO2 and 14C-lipids from 1-14C-glycerol. When the decrease in the specific activity of the tracer is considered to calculate the respective velocities, it turns out that glycerol actually enhances the rate of synthesis of both CO2 and glyceride glycerol. Glucose enhances the rate of synthesis of CO2 and fatty acids from glycerol but decreases the rate of glyceride glycerol synthesis from the same substrate. While the Km of the glycerol effect is much lower that the physiological concentrations of glycerol the Ka and Ki of the glucose effects are above or close to its concentration in blood. The results are discussed in terms of the competitive effects of glucose and glycerol for the synthesis of alpha-glycerophosphate and the necessity of glucose for lipogenesis from glycerol in adipose tissue.

Adipose Tissue↗

PubMed1975

Alpha-Glycerol phosphatase and glycerol kinase activities in tissues of the silkmoth Hyalophora cecropia during the larval-pupal transformation.

Magnesium metabolism has been studied in Hyalophora cecropia during the larval-pupal transformation (LPT) (Jungreis, A. M., Am. J. Physiol. 224: 27--30, 1973). Throughout this period, it accumulated in midgut (0.5 M at ecdysis), presumably as osmotically inactive Mg3(PO4)2. Glycerol accumulation in hemolymph was also first noted during this period. Since total alpha-glycerol phosphate present in hemolymph declined between the larval and pupal stages of development, the relationship between magnesium and alpha-glycerol phosphate metabolism was studied. Specific and total alpha-glycerol phosphatase (degradative) and glycerol kinase (synthetic) enzyme activities were measured in fat-body and midgut tissue throughout the LPT. At both feeding larval and diapause pupal stages in development in both tissues, total glycerol kinase activity is greater than that of alpha-glycerol phosphatase with degradative/synthetic activity ratios of 0.2--0.5. In fat body, ratios remained constant or shifted in the direction of synthesis during the LPT, whereas those measured in midgut tissue increased in the direction of degradation with a maximum ratio of 5.8 noted following spinning. The increase in degradative/synthetic activity ratios in midgut tissue is attributed to a greater rate of loss of glycerol kinase than alpha-glycerol phosphatase enzyme activity. Orthophosphate, presumably released from alpha-glycerol phosphate within the cells of the pharate pupal midgut tissue, combines with magnesium to form osmotically inactive Mg3(PO4)2 crystals.

Animals↗

PubMed1975

Proportional activities of glycerol kinase and glycerol 3-phosphate dehydrogenase in rat hepatomas.

The activities of glycerol 3-phosphate dehydrogenase (EC 1.1.1.8), glycerol kinase (EC 2.7.1.30), lactate dehydrogenase (EC 1.1.1.27), "malic' enzyme (L-malate-NADP+ oxidoreductase; EC 1.1.1.40) and the beta-oxoacyl-(acyl-carrier protein) reductase component of the fatty acid synthetase complex were measured in nine hepatoma lines (8 in rats, 1 in mouse) and in the livers of host animals. With the single exception of Morris hepatoma 16, which had unusually high glycerol 3-phosphate dehydrogenase activity, the activities of glycerol 3-phosphate dehydrogenase and glycerol kinase were highly correlated in normal livers and hepatomas (r = 0.97; P less than 0.01). The activities of these two enzymes were not strongly correlated with the activities of any of the other three enzymes. The primary function of hepatic glycerol 3-phosphate dehydrogenase appears to be in gluconeogenesis from glycerol.

Animals↗

PubMed1979

Conversion of (U-14C)-glycerol, (2-3H)-glycerol and (1-14C)-palmitate into circulating lipoproteins in the rat.

The in vivo formation of labelled very low density lipoproteins (VLDL) from (U-14C)-glycerol, (2-3H)-glycerol and (1-14C)-palmitate was studied in fed female rats. The rate of disappearance of radioactivity from plasma after the i.v. injection with these tracers was similar for (U-14C)-glycerol and (1-14C)-palmitate. With (2-3H)-glycerol, plasma radioactivity at 10 min was lower than with the other substrates although it did not change thereafter. A certain proportion of radioactivity administered as glycerol appeared in plasma lipids, mainly in the VLDL glyceride glycerol fraction, although when (U-14C)-glycerol was the substrate, a considerable portion also appeared in the esterified fatty acids of these lipoproteins. When using (1-14C)-palmitate, practically all the circulating labelled esterified fatty acids appeared in the VLDL fraction, while the labelled free fatty acids appeared in lipoprotein of higher density, presumable free fatty acid-albumin complexes. This data is discussed in terms of the role of the liver in the rapid, continuous cycling of these substrates to yield VLDL-glycerides for their extrahepatic utilization.

Animals↗

PubMed1975

[Effects of parenteral infusion of glycerol on glycerol kinase and adenosintriphosphate in rat kidneys (author's transl)].

Effects of intravenous glycerol infusions on glycerol kinase and adenosintriphosphate in rat kidneys. Intravenous infusions of glycerol with rates near and above the average maximal turnover capacity (0,74 g.kg-1.h-1) cause alterations of the kidneys such as weight increase, decrease of protein content and activity of glycerol kinase with excretion of this enzyme in the urine. At infusion rates of 0,6 g.kg-1.h-1 and more a decrease of the ATP-content of the kidneys is observed. Effects on the liver are not consistent and only demonstrable at infusion rates above the maximal turnover rate of glycerol. The results are discussed with regard to osmotic nephrosis. The appearance of glycerol kinase in the urine is discussed as an early symptom of kidney damage.

Adenine Nucleotides↗

PubMed1979

Biosynthesis in Escherichia coli of sn-glycerol 3-phosphate, a precursor of phospholipid. Palmitoyl-CoA inhibition of the biosynthetic sn-glycerol-3-phosphate dehydrogenase.

Homogeneous biosynthetic sn-glycerol-3-phosphate dehydrogenase (EC 1.1.1.8) of Escherichia coli was potently inhibited by palmitoyl-CoA and other long chain acyl-CoA thioesters. The concentration dependence of this inhibition was not cooperative. Enzyme activity was inhibited 50% at 1 microM palmitoyl-CoA; thus, this inhibition occurred at concentrations below the critical micellar concentration of palmitoyl-CoA. Palmitoyl-CoA was a reversible, noncompetitive inhibitor with respect to both NADPH and dihydroxyacetone phosphate. Palmitoyl-CoA did not affect the quaternary structure of the enzyme. This inhibition could be prevented or reversed by the addition of phospholipid vesicles prepared from E. coli phospholipids. Palmitoyl-CoA did not alter the kinetics of inhibition by sn-glycerol 3-phosphate, which is a proven physiological regulator of this enzyme. Decanoyl-CoA, dodecanoyl-CoA, myristoyl-CoA, palmitoyl-(1,N6-etheno)CoA, stearoyl-CoA, and oleoyl-CoA inhibited sn-glycerol-3-phosphate dehydrogenase at concentrations below their critical micellar concentrations. Palmitate inhibited sn-glycerol-3-phosphate dehydrogenase activity 50% at 200 microM. Palmitoyl-carnitine, deoxycholate, taurocholate, and dodecyl sulfate were more potent inhibitors than Triton X-100, Tween-20, or Tween-80. Palmitoyl-acyl carrier protein at concentrations up to 50 microM had no effect on sn-glycerol-3-phosphate dehydrogenase activity. The possible physiological role of long chain fatty acyl-CoA thioesters in the regulation of sn-glycerol 3-phosphate and phospholipid biosynthesis in E. coli is discussed.

Acyl Coenzyme A↗

PubMed1977

Regulation of selectivity of CDPcholine: 1,2-diacyl-sn-glycerol cholinephosphotransferase in rat liver microsomes towards different molecular species of 1,2-diacyl-sn-glycerols.

The suitability of monoenoic, dienoic, tetraenoic, and hexaenoic molecular species of 1,2-diacyl-sn-glycerols as substrates for the CDPcholine: 1,2-diacyl-sn-glycerol cholinephosphotransferase (EC 2.7.8.2) was studied in rat liver microsomes. No statistically significant difference in the rates of phosphatidylcholine synthesis with the various diacylglycerols was found at 0.40 mM, although a moderate discrimination against hexaenoic species relative to monoenoic and dienoic species was observed at 0.25 mM. The addition of palmitoyl-CoA (7.5 micron) significantly enhanced cholinephosphotransferase activity when tetraenoic diacylglycerols were added at 0.25 or 0.40 mM. CDPethanolamine at 24.4 micron was found to inhibit the rates of phophatidylcholine biosynthesis by 54 and 39% with hexaenoic and monoenoic 1,2-diacyl-sn-glycerols, respectively, whereas no significant effects were observed in the case of dienoic and tetraenoic species. These latter findings may partially explain why 1-saturated 2-docosahexaenoyl diacylglycerols are used to a greater extent for phosphatidylethanolamine than for phosphatidylcholine synthesis in rat liver in vivo. The present results also suggest that the selectivity of the cholinephosphotransferase for certain molecular species of 1,2-diacyl-sn-glycerols is a function of diacylglycerol concentration and may be mediated under physiological conditions by substrates for enzymes which compete for common diacylglycerol precursors.

Animals↗

PubMed1977

Study on the mechanism of action of adenosylcobalamin-dependent glycerol dehydratase from Aerobacter aerogenes. I. Role of structural components of adenosylcobalamin the formation of the active site of glycerol dehydratase.

A new method of partial chemical synthesis of adenosylcobalamin (Co alpha-[alpha-5,6-diemethylbenzimidazolyl)]-Co beta-adenosylcobamide, AdoCbl) analogs has been developed. A series of derivatives of AdoCbl modified in the nucleoside and nucleotide ligands and corrin macrocycle have been obtained. The interaction of AdoCl analogs with glycerol dehydratase (EC 4.2.1.30) from Aerobacter aerogenes has been investigated. It has been shown that the nucleoside ligand of AdoCbl provides no essential contribution to the binding of apoenzyme but the preservation of the exact structure of the 1-N and 2-C positions of adenine appears essential for the catalysis. The coordination bond between the Co and nucleotide ligand of AdoCl does not play a decisive role in glycerol dehydratase activity. To form the active site of the glycerol dehydrates, the nucleotide in the AdoCbl structure is essential since nucleotide elimination results in a 100-fold increase of Ki for the corresponding analog. In the binding of AdoCbl with apoenzyme, the main role belongs to the corrin macrocycle, in which the e-propionamide group is significant for binding with apoenzyme, but presumably not essential for catalysis.

Adenine Nucleotides↗

PubMedDate not supplied

Removal of HBSAg from blood in vitro. I. Effects of washing alone, glycerol addition and removal, and glycerolization, freezing, and washing.

Red blood cells from HBSAg-positive blood were washed in the Fenwal Elutramatic, Haemonetics Processor 15, or the IBM Blood Processor with sodium chloride solutions, or in the Huggins Cytoglomerator with sugar solutions. The Fenwal Elutramatic and IBM Blood Processor were the most efficient washing systems, the Haemonetics Processor 15 was less efficient, and the Huggins Cytoglomerator was the least efficient in removing the HBSAg. Washing to remove the HBSAg from red blood cells containing 40 per cent W/V glycerol in an ionic medium was more efficient than washing HBSAg from liquid-stored red blood cells or red blood cells containing 20 per cent W/V glycerol. The original and modified dilution/agglomeration wash cycles used in the Huggins Cytoglomerator were not able to remove the HBSAg from units of blood that were radioimmune assay (RIA) positive and counterelectrophoresis (CEP) negative. Freezing had no effect on the removal of the HBSAg in vitro, whereas the concentration of 40 per cent W/V glycerol in the red blood cells that were washed did. HBSAg was not found in the amorphous debris remaining in the polycarbonate disposable bowl used in the Haemonetics Processor 15 or in the microaggregates remaining in washed red blood cells.

Blood Preservation↗

PubMed1977

Study of the mechanism of action of adenosylcobalamindependent glycerol dehydratase from Aerobacter aerogenes. II. The inactivation kinetics of glycerol dehydratase complexes with adenosylobalamin and its analogs.

The inactivation kinetics of vacterial glycerol dehydratase (EC 4.2.1.30) in the course of its reaction with adenosylcobalamin (AdoCbl) and its analogs were investigated. It was shown that the inactivation rate of apoenzyme complexes with AdoCbl analogs is determined by the nature of the analogs employed and probably by the rate of their conversion into hydroxycobalamins. A possible inactivation mechanism of glycerol dehydratase is discussed.

Apoenzymes↗

PubMed1978

Comparative study of the clinical effects of vincamine + glycerol versus glycerol + placebo in the acute phase of stroke.

The treatment of the acute phase of stroke creates a difficult problem to the clinician. The presently used drugs lead to controversial results. The progress in knowledge of the pathogenesis of cerebral damage underlines the determinant role of the metabolic deficits in the ischemic areas. The effect on the clinical symptomatology of patients in the acute phase of stroke was studied during a double-blind comparative clinical trial with an alcaloid of Vinca minor (Pervincamine) which acts favorably against disturbances of oxydative glucose metabolism and of cerebral microcirculation. 20 patients divided into two homogeneous groups received during 5 days either Pervincamine (4 ampoules of 3 ml = 60 mg vincamine p.d.) + glycerol, or glycerol + placebo administered by i.v. infusion. Clinically the results indicate a greater improvement of the neurological status (objectivated by a neurological scale) with vincamine treatment than with placebo. Statistically the analysis confirms the highly significant effect of vincamine on motility of lower and upper limbs (p less than 0.02) and the significant effect on cranial nerves (homonymous hemianopsia and conjugated deviation of eyes) (p less than 0.05) and on the sphincter control level (p less than 0.05).

Adult↗

PubMed1979