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PubMed1976

Phosphorylation of glycerol and dihydroxyacetone in Acetobacter xylinum and its possible regulatory role.

Extracts of Acetobacter xylinum catalyze the phosphorylation of glycerol and dihydroxyacetone (DHA) by adenosine 5'-triphosphate (ATP) to form, respectively, L-alpha-glycerophosphate and DHA phosphate. The ability to promote phosphorylation of glycerol and DHA was higher in glycerol-grown cells than in glucose- or succinate-grown cells. The activity of glycerol kinase in extracts is compatible with the overall rate of glycerol oxidation in vivo. The glycerol-DHA kinase has been purified 210-fold from extracts, and its molecular weight was determined to be 50,000 by gel filtration. The glycerol kinase to DHA kinase activity ratio remained essentially constant at 1.6 at all stages of purification. The optimal pH for both reactions was 8.4 to 9.2. Reaction rates with the purified enzyme were hyperbolic functions of glycerol, DHA, and ATP. The Km for glycerol is 0.5 mM and that for DHA is 5 mM; both are independent of the ATP concentration. The Km for ATP in both kinase reactions is 0.5 mM and is independent of glycerol and DHA concentrations. Glycerol and DHA are competitive substrates with Ki values equal to their respective Km values as substrates. D-Glyceraldehyde and l-Glyceraldehyde were not phosphorylated and did not inhibit the enzyme. Among the nucleotide triphosphates tested, only ATP was active as the phosphoryl group donor. Fructose diphosphate (FDP) inhibited both kinase activities competitively with respect to ATP (Ki= 0.02 mM) and noncompetitively with respect to glycerol and DHA. Adenosine 5'-diphosphate (ADP) and adenosine 5'-monophosphate (AMP) inhibited both enzymic activities competitively with respect to ATP (Ki (ADP) = 0.4 mM; Ki (AMP) =0.25 mM). A. xylinum cells with a high FDP content did not grow on glycerol. Depletion of cellular FDP by starvation enabled rapid growth on glycerol. It is concluded that a single enzyme from A. xylinum is responsible for the phosphorylation of both glycerol and DHA. This as well as the sensitivity of the enzyme to inhibition by FDP and AMP suggest that it has a regulatory role in glycerol metabolism.

Adenosine Diphosphate↗
PubMed1975

Mutants of Escherichia coli defective in membrane phospholipid synthesis. Properties of wild type and Km defective sn-glycerol-3-phosphate acyltransferase activities.

The sn-glycerol-3-phosphate (glycerol-P) acyltransferase, the first enzyme of membrane phospholipid synthesis in Escherichia coli, was investigated in a wild type and a mutant strain defective in this activity. The mutant strain, selected as a glycerol-P auxotroph, was previously shown to contain a glycerol-P acyltransferase activity with an apparent Km for glycerol-P 10 times higher than that of its parent or revertants. The membranous mutant glycerol-P acyltransferase but did not appear to be thermolabile in vivo. Revertants no longer requiring glycerol-P for growth, showed glycerol-P acyltransferase activity with thermolability properties similar to the wild type. The second phospholipid biosynthetic enzyme, 1-acylglycerol-P acyltransferase, was not thermolabile in membranes containing a thermolabile glycerol-P acyltransferase activity. The pH optimum for the mutant acyltransferase was over 1 pH unit higher than that of the parental activity. Further, the mutant and wild type glycerol-P acyltransferase differed in their response to magnesium chloride and potassium chloride. The palmitoyl-CoA dependence of the wild type and mutant glycerol-P acyltransferase activities were different. The mutant glycerol-P acyltransferase activity was inhibited greater than 90% by Triton X-100 under conditions where the wild type activity was not affected. These experiments provide novel information about the wild type glycerol-P acyltransferase activity of E. coli and provide six additional lines of evidence for the mutant character of the glycerol-P acyltransferase in the mutant strains.

Acyltransferases↗
PubMed1976

Effect of glycerol on lipogenic enzyme activities and on fatty acid synthesis in the rat and chicken.

The influence of glycerol on the rates of fatty acid snythesis in liver slices from rats and chickens in pieces of adipose tissue from rats was first studied. Then the effect of dietary glycerol on lipid metabolism in rats and cheickens was examined. Media containing 3 or 10 mM glycerol depressed the rate of glucose conversion to fatty acids in rat liver slices. However, media containing up to 25 mM glycerol did not influence the rate of fatty acid synthesis in chick liver slices. The inhibitory action of glycerol in rat liver slices might occur at the level of glucose (or glycogen) conversion to pyruvate because glycerol did not inhibit pyruvate or acetate conversion to fatty acids. Rats and chickens were fed glycerol containing diets for either 3 days or 3 weeks. Feeding diets containing 20.5 parts glycerol (22% of dietary energy) to rats or chickens did not influence the growth rate of the animals. However, substitution of 42.2 parts glycerol (43% of dietary energy) for glucose in the diet significantly depressed food intake and growth rate in both rats and chickens. The activities of citrate cleavage enzyme, fatty acid synthetase and malic enzyme in livers of rats fed the glycerol-containing diets were dramatically increased. However, this stimulation of enzyme activity occurred without a concomitant increase in the in vivo rate of fatty acid synthesis in the rat liver. In the chicken, unlike the rat, dietary glycerol did not stimulate but instead decreased hepatic malic enzyme and fatty acid synthetase activities. No significant differences in adipose tissue lipogenic enzyme activities or in the rates of fatty acid synthesis were observed in rats fed glycerol-containing diets. The lipogenic response to glycerol feeding depends on the species as well as the organ.

ATP Citrate (pro-S)-Lyase↗
PubMed1976

Enhancement of sperm acrosin activity by glycerol-pretreatment - quantitative estimations.

Acetic acid treatment of spermatozoa, a method suitable for optimal extraction of the acrosomal proteinase acrosin, was used to show the influence of glycerol on sperm acrosin activity. Short-time pretreatment of semen samples with glycerol in concentrations up to 35% (v/v) caused a 1.5-2.5 fold increase in sperm acrosin activity. Higher glycerol concentrations caused a decrease in sperm acrosin activity due to leakage of the enzyme into the suspension medium. A further increase in sperm acrosin activity was observed during aging of semen in the presence of glycerol. In this case, the height of the increase depends on the glycerol concentration applied as well as incubation temperature and time. The acrosin activation pattern induced by glycerol was not influenced by proteinase (acrosin) inhibitors. On the other hand, addition of glycerol to spermatozoa from which the seminal plasma had been removed and substituted by physiological saline caused only a small increase in sperm acrosin activity. This indicates the occurrence of a seminal plasma factor which is either stimulated (activated) by glycerol or which can penetrate the membranes and subsequently activate acrosin only in the presence of glycerol. This seminal plasma factor was not consumed during activation and could be transfered to another sperm sample. However, a protecting influence of such a factor on the sperm head membranes and thus an indirect activation effect, i.e. better extractibility of acrosin, has also to be considered. The glycerol-induced rise of the acrosin activity is not caused by reversible conformational changes of the enzyme molecules: acrosin activity was not diminished if glycerol was removed from semen samples or extracts later on. The possibility that the observed increase in BAEE-splitting activity is due to a so far unknown proteinase may be excluded: the activity completely disappeared by neutralization due to formation of the acrosin-inhibitor complex and appeared again by acidification, a well known characteristic of acrosin and its inhibitors. Factors which are probably responsible for the glycerol-induced activation of acrosin-membrane effects and the activation of a precursor from of acrosin-are discussed.

Acrosin↗
PubMed1975

Kinetics of glycerol uptake by the perfused rat liver. Membrane transport, phosphorylation and effect on NAD redox level.

The kinetics of glycerol uptake by the perfused rat liver were determined according to a model which includes membrane transport, intracellular phosphorylation and competitive inhibition of glycerol phosphorylation by L-glycerol 3-phosphate. The membrane transport obeys first-order kinetics at concentrations below 10 mM in the affluent medium. The K-m of the glycerol phosphorylation was 10 muM and the K-i of the L-glycerol 3-phosphate inhibition was 50 muM. The maximum activity (V) was 3.70 mumoles/min per g liver wet wt. These results are similar to in vitro kinetics of the glycerol kinase, except that K-i was found to be somewhat lower in the intact organ. At low glycerol concentrations, a steep concentration gradient exists across the liver cell membrane. The increase in the lactate to pyruvate concentration ratio during glycerol metabolism is related to the actual concentration of L-glycerol 3-phosphate, not to the rate of glycerol uptake.

Animals↗
PubMed1978

Stopped-flow spectrophotometric assay of glycerol permeation in Escherichia coli: applicability and limitations.

The passive permeation and facilitated diffusion of glycerol in various strains of Escherichia coli have been studied by stopped-flow spectrophotometry. Contrary to the prediction for glycerol entry by simple diffusion, the reciprocal relaxation time (1/tau, s-1) for the passive permeation of glycerol in cells grown in the presence of glucose was not constant but decreased as the glycerol concentration increased above 100 mM. This anomaly was not due to refractive index differences or to the presence of residual levels of the glycerol facilitator protein in non-induced cells. Although reciprocal relaxation times for glycerol-induced E. coli exhibited the expected elevation relative to non-induced cells, a similar anomalous decrease 1/tar (s-1) with increasing glycerol concentration was observed. In addition, at early times after suspension in dilute buffer, the 1/tau (s-1) values obtained for induced or non-induced E. coli swelling in glycerol were considerably greater than for organisms incubated in dilute buffer for longer times. We concluded that either this spectrophotometric technique was not monitoring solely the permeation of glycerol into E. coli, or concentrations of glycerol above 100 mM significantly perturbed the structure of the E. coli cell envelope.

Cell Count↗
PubMed1978

Relationship between catabolism of glycerol and metabolism of hexosephosphate derivatives by Pseudomonas aeruginosa.

The relationship between catabolism of glycerol and metabolism of hexosephosphate derivatives in Pseudomonas aeruginosa was studied by comparing the growth on glycerol and enzymatic constitution of strain PAO with these characteristics of glucose-catabolic mutants and revertants. Growth of strain PAO on glycerol induced a catabolic oxidized nicotinamide adenine dinucleotide-linked glyceraldehyde-phosphate dehydrogenase and seven glucose-catabolic enzymes. The results indicated that these enzymes were induced by a six-carbon metabolite of glucose. All strains possessed a constitutive anabolic Embden-Meyerhof-Parnas pathway allowing limited conversion of glycerol-derived triosephosphate to hexosephosphate derivatives, which was consistent with induction of these enzymes by glycerol. Phosphogluconate dehydratase-deficient mutants grew on glycerol. However, mutants lacking both phosphogluconate dehydrogenase and phosphogluconate dehydratase were unable to grow on glycerol, although these strains possessed all of the enzymes needed for degradation of glycerol. These mutants apparently were inhibited by hexosephosphate derivatives, which originated from glycerol-derived triosephosphate and could not be dissimilated. This conclusion was supported by the fact that revertants regaining only a limited capacity to degrade 6-phosphogluconate were glycerol positive but remained glucose negative.

Gluconates↗
PubMed1976

Triacylglycerol synthesis in isolated fat cells. Evidence that the sn-glycerol-3-phosphate and dihydroxyacetone phosphate acyltransferase activities are dual catalytic functions of a single microsomal enzyme.

The acyl-CoA:sn-glycerol-3-phosphate acyltransferase (EC 2.3.1.15) (glycerol-P acyltransferase) and acyl-CoA:dihydroxyacetone phosphate acyltransferase (EC 2.3.1.42) (DHAP acyltransferase) activities were investigated in vitro in order to evaluate the quantitative contribution of the glycerol-P and DHAP pathways for the synthesis of triacylglycerols in isolated fat cells and to test the hypothesis that these two activities may be dual catalytic functions of a single enzyme. More than 85% of both acyltransferase activities was associated with the microsomal subcellular fraction. The microsomal glycerol-P acyltransferase activity showed an apparent Km of 8 muM for glycerol-P with a Vmax of 15.6 nmol/min/mg, while the DHAP acyltransferase activity showed an apparent Km of 40 muM for DHAP with a Vmax of 9.7 nmol/min/mg. Glycerol-P was a competitive inhibitor (Ki = 7.2 muM) of the DHAP acyltransferase, and DHAP was a competitive inhibitor (Ki = 92 muM) of the glycerol-P acyltransferase. The two acyltransferase activities showed virtual identity in their pH dependence, acyl-CoA chain length dependence, thermolability, and inactivation by N-ethylmaleimide. Trypsin, detergents, collagenase, phospholipases, and various salts and organic solvents also had similar effects on both activities. Taken as a whole, the data strongly suggest that the microsomal glycerol-P and DHAP acyltransferase activities actually represent dual functions of a single enzyme. Calculations based on the above kinetic constants and previously reported glycerol-P and DHAP pools in adipocytes suggest that the in vivo ratio of glycerol-P to DHAP acylation should be greater than 24:1.

Acyltransferases↗
PubMed1976

On the mechanism of salt tolerance. Production of glycerol and heat during growth of Debaryomyces hansenii.

As glycerol was suggested as an osmotic agent in the salt tolerant Debaryomyces hansenii the concentrations of total, intracellular, and extracellular glycerol produced by this yeast was followed during growth in 4 mM, 0.68 M, and 2.7 M NaCl media. The total amount of glycerol was not directly proportional to biomass production but to the cultural salinity with maximum concentrations just prior to or at the beginning of the stationary phase. In all cultures the cells lost some glycerol to the media, at 2.7 M NaCl the extracellular glycerol even amounted maximally to 80% of the total. A distinct maximum of intracellular glycerol, related to dry weight or cell number, appeared during the log phase at all NaCl concentrations. As the intracellular calculated glycerol concentrations amounted to 0.2 M, 0.8 M, and 2.6 M in late log phase cells at 4mM, 0.68 M, and 2.7 M NaCl, respectively, whereas the corresponding analysed values for the glycerol concentrations of the media were 0.7 mM, 2.5 mM, and 3.0 mM, glycerol contributes to the osmotic balance of the cells. During the course of growth all cultures showed a decreasing heat production related to cell substance produced, most pronounced at 2.7 M NaCl. At 2.7 M NaCl the total heat production amounted to--1690 kJ per mole glucose consumed in contrast to--1200 and--1130 kJ at 4 mM and 0.68 M NaCl, respectively. The Ym-values were of an inverse order, being 129, 120, and 93 at 4 mM, 0.68 M, and 2.7 M NaCl respectively.

Ascomycota↗
PubMed1976

Effects of glycerol on VLDL secretion by the isolated rat liver.

Stimulation of VLDL production by increasing fatty acid availability is now well established. However, a possible regulatory role of glycerol, another lipid precursor, in VLDL synthesis by the liver has not yet been substaniated. The present experiments investigate this problem using the isolated perfused rat liver. [14C] Glycerol uptake and metabolism were studied at two different glycerol concentrations: 1 mumol/perfusate (control) or 1.6 mmol/perfusate. VLDL production and lipid synthesis were investigated using [14C]leucine and several labelled fatty acids as precursors in control and glycerol-overloaded livers. Neoglycogenesis and lipogenesis from glycerol carbons are negligible in our conditions. The absolute amount of glycerol, but not the precentage, taken up by the liver, increased after raising its concentration in the perfusate. A major part of exogenous (plasmatic) glycerol was esterified with endogenous (non plasmatic) fatty acids. Incorporation of radioactive fatty acids into liver or plasma lipids was lower than in the the control group. Significant differences were observed between saturated and unsaturated fatty acids used as lipid precursors. Production of VLDL as assessed by radioactive leucine and fatty acid incorporation in the VLDL of the perfusate was depressed by glycerol. Glycerol partly inhibits the normal stimulation of VLDL production by plasmatic fatty acid overload.

Animals↗
PubMed1977

Immunochemical evidence for the difference between coenzyme-B12-dependent diol dehydratase and glycerol dehydratase.

Klebsiella pneumoniae ATCC 25955 (formerly named Aerobacter aerogenes PZH 572, Warsaw), which is known to produce coenzyme-B12-dependent glycerol dehydratase when grown anaerobically in a glycerol medium, formed coenzyme-B12-dependent diol dehydratase in a 1,2-propanediol-containing medium. Both the diol dehydratase and the glycerol dehydratase produced by the organism catalyzed the conversion of glycerol, 1,2-propanediol and 1,2-ethanediol to the corresponding aldehydes and underwent concomitant inactivation during the catalysis of glycerol dehydration, as does the diol dehydratase of K. pneumoniae (A. aerogenes) ATCC 8724. However, the two enzymes were distinguishable from each other by the monovalent-cation-selectivity pattern and by substrate specificity; that is, glycerol dehydratase preferred glycerol to 1,2-propanediol as a substrate, whereas diol dehydratase preferred 1,2-propanediol to glycerol, as judged from initial velocity studies. Ouchterlony double-diffusion analysis and immunochemical titration with rabbit antiserum against diol dehydratase of K. pneumoniae ATCC 8724 established clearly that the diol dehydratase of K. pneumoniae ATCC 25955 is immunologically similar to that of K. pneumoniae ATCC 8724, while the glycerol dehydratase of the former is different from the diol dehydratase of both strains. Both the enzymes were found to be distributed in several bacteria of the family Enterobacteriaceae.

Cations, Monovalent↗
PubMed1976

Glycerol transport in human red cells.

The kinetics of 14C-glycerol exchange was studied in human red cells. Glycerol appeared to be transported by two mechanisms: (i) by facilitated diffusion with permeability depending on glycerol concentration, and (ii) by an unspecific pathway, presumably representing the diffusion of individual glycerol molecules through the membrane with permeability independent of glycerol concentration. The latter permeability was 8 X 10(-8) cm/s at 20 degrees C, it was independent of pH, and had an activation energy of 25 kcal/mol. The facilitated transport of glycerol was completely inhibited by Cu++, and the activation energy was low, about 10 kcal/mol. The transport system was competitively inhibited by H+, reacting with at least three hydrogen analogue, as well as dimethylsulfoxide (a hydrogen bonding molecule with no structural resemblance to glycerol), inhibited glycerol transport competitively. Steins "dimerizer hypothesis" was revised according to our findings. A kinetic scheme describing the reactions of a transport controlling site with glycerol is presented in the Appendix. It is demonstrated in the article that the scheme accounts for out experimental results.

Biological Transport↗
PubMed1978

Glycerolipid biosynthesis in Saccharomyces cerevisiae: sn-glycerol-3-phosphate and dihydroxyacetone phosphate acyltransferase activities.

Yeast acyl-coenzyme A:dihydroxyacetone-phosphate O-acyltransferase (DHAP acyltransferase; EC 2.3.1.42) was investigated to (i) determine whether its activity and that of acyl-coenzyme A:sn-glycerol-3-phosphate O-acyltransferase (glycerol-P acyltransferase; EC 2.3.1.15) represent dual catalytic functions of a single membranous enzyme, (ii) estimate the relative contributions of the glycerol-P and DHAP pathways for yeast glycerolipid synthesis, and (iii) evaluate the suitability of yeast for future genetic investigations of the eucaryotic glycerol-P and DHAP acyltransferase activities. The membranous DHAP acyltransferase activity showed an apparent Km of 0.79 mM for DHAP, with a Vmax of 5.3 nmol/min per mg, whereas the glycerol-P acyltransferase activity showed an apparent Km of 0.05 mM for glycerol-P, with a Vmax of 3.4 nmol/min per mg. Glycerol-P was a competitive inhibitor (Ki, 0.07 mM) of the DHAP acyltransferase activity, and DHAP was a competitive inhibitor (Ki, 0.91 mM) of the glycerol-P acyltransferase activity. The two acyltransferase activities exhibited marked similarities in their pH dependence, acyl-coenzyme A chain length preference and substrate concentration dependencies, thermolability, and patterns of inactivation by N-ethylmaleimide, trypsin, and detergents. Thus, the data strongly suggest that yeast glycerol-P and DHAP acyltransferase activities represent dual catalytic functions of a single membrane-bound enzyme. Furthermore, since no acyl-DHAP oxidoreductase activity could be detected in yeast membranes, the DHAP pathway for glycerolipid synthesis may not operate in yeast.

Acyl Coenzyme A↗
PubMed1978

Incorporation of labelled glucose and glycerol into phospholipids and triglycerides by rat and rabbit aorta.

[1-14C]Glycerol and [U1-14C]glucose were incorporated into aortic phospholipids and triglycerides by isolated rat and rabbit aorta. The major portion of radioactivity was found in the glycerol moiety of triglycerides and phospholipids. Within the range of concentrations studied the rate of incorporation of [1-14C]glycerol was dependent on substrate concentration, whereas the rate of incorporation of [U1-14C]glucose was not. The distribution of radioactivity in the glycerophosphatides was found mainly in phosphatidylserine and phosphatidic acid when [1-14C]glycerol was used as substrate. On the other hand, the major portion of radioactivity was found in phosphatidylcholine when [U1-14C]glucose was the substrate. The incorporation of [1-14C]glycerol and [U1-14C]glucose into aortic triglycerides and phospholipids was markedly increased by aortae obtained from rabbits fed an atherogenic diet as compared to aortae from control animals. Results from double-labeled glycerol containing both [2-3H]glycerol and [1-14C]glycerol indicated that the biosynthesis of triglycerides and phospholipids in the rat aorta did not use phosphatidic acid from the same pool.

Animals↗
PubMed1978

Physical-chemical basis of the protection of slowly frozen human erythrocytes by glycerol.

One theory of freezing damage suggests that slowly cooled cells are killed by being exposed to increasing concentrations of electrolytes as the suspending medium freezes. A corollary to this view is that protective additives such as glycerol protect cells by acting colligatively to reduce the electrolyte concentration at any subzero temperature. Recently published phase-diagram data for the ternary system glycerol-NaCl-water by M. L. Shepard et al. (Cryobiology,13:9-23, 1976), in combination with the data on human red cell survival vs. subzero temperature presented here and in the companion study of Souzu and Mazur (Biophys. J.,23:89-100), permit a precise test of this theory. Appropriate liquidus phase-diagram information for the solutions used in the red cell freezing experiments was obtained by interpolation of the liquidus data of Shepard and his co-workers. The results of phase-diagram analysis of red cell survival indicate that the correlation between the temperature that yields 50% hemolysis (LT(50)) and the electrolyte concentration attained at that temperature in various concentrations of glycerol is poor. With increasing concentrations of glycerol, the cells were killed at progressively lower concentrations of NaCl. For example, the LT(50) for cells frozen in the absence of glycerol corresponds to a NaCl concentration of 12 weight percent (2.4 molal), while for cells frozen in 1.75 M glycerol in buffered saline the LT(50) corresponds to 3.0 weight percent NaCl (1.3 molal). The data, in combination with other findings, lead to two conclusions: (a) The protection from glycerol is due to its colligative ability to reduce the concentration of sodium chloride in the external medium, but (b) the protection is less than that expected from colligative effects; apparently glycerol itself can also be a source of damage, probably because it renders the red cells susceptible to osmotic shock during thawing.

Buffers↗
PubMed1976

The effect of glucose, insulin and adrenaline on glycerol metabolism in vitro in rat adipose tissue.

The uptake and utilization of [1-14C]glycerol was determined in pieces of rat epididymal fat-pads incubated in Krebs--Ringer bicarbonate buffer containing albumin. Insulin (200 muunits/ml), adrenaline (epinephrine; 0.5 mug/ml) and glucose (0, 5, 15 and 20 mM) were added to the medium. Changes in the specific radioactivity of the tracer during the incubation were taken into account in calculating the rate of glycerol utilization. Adrenaline decreased glycerol uptake, whereas insulin plus adrenaline increased it. The rate of incorporation of glycerol into glycerides was decreased by adrenaline and insulin, singly or together. Insulin increased the rate of formation of CO2 and fatty acids from glycerol. The formation of CO2 and fatty acids was further enhanced by insulin plus adrenaline. The decrease in glycerol uptake induced by adrenaline, the decrease in incorporation of glycerol into glycerides induced by insulin and insulin plus adrenaline and the synthesis of fatty acids were dependent on the presence of glucose in the medium. Thus insulin and adrenaline act on glycerol utilization in adipose tissue and some of their effects are mediated by action on glucose metabolism, but others are independent of this.

Adipose Tissue↗
PubMed1977

Some effects, in baboons, of chronic ingestion of glycerol with sucrose or glucose.

Six mature male and six mature female baboons were given fat-free diets high in sucrose or glucose together with glycerol, a chow diet with glycerol, and a fat-free high sucrose diet without glycerol. In the male animals, the concentration of triglyceride, cholesterol, glucose, and glycerol in fasting serum was significantly greater when sucrose and glycerol were given together compared with the other diets. The fasting serum triglyceride and cholesterol were significantly greater in the females on the sucrose + glycerol diet compared to the glucose + glycerol diet. It is suggested that glycerol and fructose (in sucrose) share a metabolic pathway that leads to an enhancement of serum lipid concentrations.

Animals↗
PubMed1976

Periplasmic protein related to the sn-glycerol-3-phosphate transport system of Escherichia coli.

Two-dimensional gel electrophoresis of shock fluids of Escherichia coli K-12 revealed the presence of a periplasmic protein related to sn-glycerol-3-phosphate transport (GLPT) that is under the regulation of glpR, the regulatory gene of the glp regulon. Mutants selected for their resistance to phosphonomycin and found to be defective in sn-glycerol-3-phosphate transport either did not produce GLPT or produced it in reduced amounts. Other mutations exhibited no apparent effect of GLPT. Transductions of glpT+ nalA phage P1 into these mutants and selection for growth on sn-glycerol-3-phosphate revealed a 50% cotransduction frequency to nalA. Reversion of mutants taht did not produce GLPT to growth on sn-glycerol-3-phosphate resulted in strains that produce GLPT. This suggests a close relationship of GLPT to the glpT gene and to sn-glycerol-3-phosphate transport. Attempts to demonstrate binding activity of GLPT in crude shock fluid towards sn-glycerol-3-phosphate have failed so far. However, all shock fluids, independent of their GLPT content, exhibited an enzymatic activity that hydrolyzes under the conditions of the binding assay, 30 to 60% of the sn-glycerol-3-phosphate to glycerol and inorganic orthophosphate.

Bacterial Proteins↗