Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Glycerol”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 55 records · Page 3Linked to original sources

Effect of glycerol on intracellular virus survival: implications for the clinical use of glycerol-preserved cadaver skin.

Glycerol has long been used for the preservation of skin allografts. The antimicrobial activity of glycerol has not been fully documented. This paper reports the results of an investigation of a model studying the effect of glycerol on the inactivation of intracellular viruses. Two viruses--herpes simplex type I (HSV-1) and poliovirus--were cultured within human dermal fibroblasts. These intracellular viruses were incubated with 50 per cent, 85 per cent and 98 per cent glycerol at 4 degrees C and 20 degrees C for 4 weeks. Each week, the cultures in glycerol and controls in fibroblast maintenance medium were assayed for virus infectivity by examining the ability of harvested viruses to infect further fibroblasts. At 4 degrees C, 85 per cent glycerol could not fully inactivate intracellular HSV-I or poliovirus even after 4 weeks; 98 per cent glycerol inactivated intracellular HSV-I (after 3 weeks) but could not fully inactivate intracellular poliovirus after 4 weeks. At 20 degrees C, 85 per cent glycerol inactivated intracellular HSV-I (within 1 week) but could not fully inactivate intracellular poliovirus after 4 weeks; 98 per cent glycerol inactivated intracellular HSV-I (within 1 week) and inactivated intracellular poliovirus (after 2 weeks). It is suggested that, on the basis of this study, glycerol can reduce intracellular virus infectivity but that its effects are very dependent on concentration, time and temperature such that we would recommend that allograft skin be exposed to 98 per cent glycerol for a minimum of at least 4 weeks at a minimum temperature of 20 degrees C before clinical use.

Cadaver↗

Oxidation of glycerol to formaldehyde by microsomes: are glycerol radicals produced in the reaction pathway?

Microsomes and reconstituted systems containing cytochrome P450 can oxidize glycerol to formaldehyde in a reaction catalyzed by an oxidant produced from the interaction of nonheme iron with H2O2. To evaluate the mechanism for this oxidation, the generation of glycerol radicals by various systems was compared to rates of formaldehyde production from glycerol. Photolysis of H2O2, oxidation of xanthine by xanthine oxidase in the presence of iron catalysts, or NADPH-dependent microsomal electron transfer in the presence of ferric-EDTA produced hydroxyl radicals. In the presence of glycerol these reaction systems produced DMPO-glycerol radical adducts which were detected by ESR spectroscopy. Despite the production of .OH and glycerol spin-trapped adducts by these reaction systems, very low amounts or nondetectable amounts of formaldehyde were produced from the glycerol. However, significant amounts of formaldehyde were observed when microsomes were incubated in the presence of ferric ammonium sulfate or ferric-ATP, although .OH production was lower with these iron catalysts than with ferric-EDTA. These results fail to support correlation between .OH production and oxidation of glycerol to formaldehyde. Under conditions in which glycerol was oxidized to formaldehyde, no glycerol radical species could be observed with DMPO as the spin-trapping agent. These results suggest the oxidant (not .OH) derived from the interaction of H2O2 with iron apparently cleaves glycerol to formaldehyde without the formation of a radical intermediate. Alternatively, the radical intermediate may be produced at a too low concentration to be detected or the radical intermediate may not be formed as a free species and therefore cannot be spin-trapped.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

The quantification of gluconeogenesis in healthy men by (2)H2O and [2-(13)C]glycerol yields different results: rates of gluconeogenesis in healthy men measured with (2)H2O are higher than those measured with [2-(13)C]glycerol.

The quantification of gluconeogenesis (GNG) by (2)H2O and [2-(13)C]glycerol and the mass isotopomer dilution analysis of glucose does not involve assumptions regarding the enrichment of the oxaloacetate precursor pool. To compare these two methods we measured GNG in six healthy postabsorptive males under identical, strictly standardized, eucaloric conditions, once after oral administration of (2)H2O and once during a primed continuous infusion of [2-(13)C]glycerol. Endogenous glucose production (EGP) was measured by infusion of [6,6-(2)H(2)]glucose. EGP was not different after (2)H2O administration or during [2-(13)C]glycerol infusion (12.2 +/- 0.7 vs. 11.7 +/- 0.3 micromol/kg.min). However, GNG measured after (2)H2O administration was significantly higher than that during [2-(13)C]glycerol infusion (7.4 +/- 0.7 vs. 4.9 +/- 0.6 micromol/kg.min; P = 0.03), representing approximately 60% and 41% of EGP, respectively. The (2)H2O study was repeated during primed continuous infusion of unlabeled glycerol, showing that infusion of glycerol at the rate used in the [2-(13)C]glycerol method does not affect the measurement of GNG with (2)H2O, viz. 7.4 +/- 0.7 without glycerol vs. 7.6 +/- 0.9 micromol/kg.min with glycerol, representing approximately 60% vs. 62% of EGP. In conclusion, GNG measured by (2)H(2)O yields higher results than those measured by [2-(13)C]glycerol. This discrepancy is not merely caused by infusion of glycerol per se. Rather, the discrepancy between both methods probably relates to conceptual problems in underlying assumptions in one or both methods.

Adult↗

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↗

A sequence variation in the mitochondrial glycerol-3-phosphate dehydrogenase gene is associated with increased plasma glycerol and free fatty acid concentrations among French Canadians.

FAD-dependent glycerol-3-phosphate dehydrogenase (mGPD) enzyme is located in the mitochondrial inner membrane where it catalyzes irreversible oxidation reactions. Type 2 diabetes mellitus (DM) is a multifactorial disorder associated with physiological abnormalities in the glycerol and free fatty acids (FFA) metabolic pathways. In the present study, we have evaluated the association among the mGPD H264R sequence variation and postabsorptive plasma FFA and glycerol concentrations in a sample of French Canadians with and without type 2 DM. A sample of 81 recently diagnosed type 2 DM and 318 nondiabetic, nonobese, normotriglyceridemic French Canadians were screened for the presence of the mGPD H264R genetic variant using a PCR-RFLP-based method. The 318 nondiabetic subjects were free of known type 2 DM covariates (fasting glucose <7.0 mmol/L, body mass index <29 kg/m(2), fasting glycerol <2.0 mmol/L and absence of the N288D sequence variation in the glycerol kinase gene, fasting triglyceride <2.5 mmol/L). The association of mGPD H264R sequence variation with plasma FFA and glycerol concentrations was assessed in different regression models. Among non-DM individuals, the R allele (HR and RR genotypes) was associated with increased plasma FFA and glycerol concentrations (P < 0.05). However, the mean plasma FFA and glycerol concentrations were not affected by the H264R genotype in the type 2 DM sample. Overall, mean plasma FFA concentrations in non-DM RR homozygotes reached values that were similar to those achieved in patients with type 2 diabetes (0.87 +/- 0.63 vs 0.90 +/- 0.48 mmol/L). After controlling for age, gender, body mass index, fasting glucose, and fasting triglyceride concentrations, the relative odds of having fasting plasma FFA levels above the 90th percentile (0.9 mmol/L) in the absence of DM was increased by twofold in H264R heterozygotes (P = 0.04) and fourfold among R264 homozygotes (P = 0.009) compared to noncarriers. In the absence of DM, the mGPD R allele was also associated with higher plasma glycerol concentrations (P < 0.05). Results in non-DM individuals suggest that the mGPD R allele is associated with DM intermediate phenotypes. The absence of a relation between mGPD genotype and DM is in accordance with the view that DM is a complex phenotype in which increased plasma FFA or glycerol concentrations result from metabolic alterations which might obscure the effect of the mGPD polymorphism.

Adult↗

Freeze resistance in rainbow smelt (Osmerus mordax): seasonal pattern of glycerol and antifreeze protein levels and liver enzyme activity associated with glycerol production.

Rainbow smelt (Osmerus mordax) inhabit inshore waters along the North American Atlantic coast. During the winter, these waters are frequently ice covered and can reach temperatures as low as -1.9 degrees C. To prevent freezing, smelt accumulate high levels of glycerol, which lower the freezing point via colligative means, and antifreeze proteins (AFP). The up-regulation of the antifreeze response (both glycerol and AFP) occurs in early fall, when water temperatures are 5 degrees -6 degrees C. The accumulation of glycerol appears to be the main mechanism of freeze resistance in smelt because it contributes more to the lowering of the body's freezing point than the activity of the AFP (0.5 degrees C vs. 0.25 degrees C for glycerol and AFP, respectively) at a water temperature of -1.5 degrees C. Moreover, AFP in smelt appears to be a safeguard mechanism to prevent freezing when glycerol levels are low. Significant increases in activities of the liver enzymes glycerol 3-phosphate dehydrogenase (GPDH), alanine aminotransferase (AlaAT), and phosphoenolpyruvate carboxykinase (PEPCK) during the initiation of glycerol production and significant correlations between enzyme activities and plasma glycerol levels suggest that these enzymes are closely associated with the synthesis and maintenance of elevated glycerol levels for use as an antifreeze. These findings add further support to the concept that carbon for glycerol is derived from amino acids.

Alanine Transaminase↗

A specific receptor site for glycerol, a new sweet tastant for Drosophila: structure-taste relationship of glycerol in the labellar sugar receptor cell.

Glycerol, a linear triol, is a sweet tastant for mammals but it has not previously been recognized to stimulate the sense of taste in insects. Here we show by electrophysiological experimentation that it effectively stimulates the labellar sugar receptor cell of Drosophila. We also show that in accord with the electrophysiological observations, the behavioral feeding response to glycerol is dose dependent. 3-Amino-1,2-propanediol inhibited the response of the sugar receptor cell to glycerol, specifically and competitively, while it had almost no effect on responses to sucrose, D-glucose, D-fructose and trehalose. In the null Drosophila mutant for the trehalose receptor (DeltaEP19), the response to glycerol showed no change, in sharp contrast with a characteristic drastic decrease in the response to trehalose. The glycerol concentration-response curves for I-type and L-type labellar hairs were statistically indistinguishable, while those for sucrose, D-glucose, D-fructose and trehalose were clearly different. These all indicate the presence of a specific receptor site for glycerol. The glycerol site was characterized by comparing the effectiveness of various derivatives of glycerol. Based on this structure-taste relationship of glycerol, a model is proposed for the glycerol site including three subsites and two steric barriers, which cannot accommodate carbon-ring containing sugars such as D-glucose.

Animals↗

Intraorganelle localization and substrate specificities of the mitochondrial acyl-CoA: sn-glycerol-3-phosphate O-acyltransferase and acyl-CoA: 1-acyl-sn-glycerol-3-phosphate O-acyltransferase from potato tubers and pea leaves.

The mitochondrial sn-glycerol-3-phosphate and 1-acyl-sn-glycerol-3-phosphate O-acyltransferases from potato tubers and pea leaves were investigated with respect to their intraorganelle localization, their positional and substrate specificities, and their fatty acid selectivities. In mitochondria from potato tubers both enzymes were found to be located in the outer membrane. The 1-acyl-sn-glycerol-3-phosphate O-acyltransferase of pea mitochondria showed the same intraorganelle localization whereas the sn-glycerol-3-phosphate O-acyltransferase behaved like a soluble protein of the intermembrane space. The sn-glycerol-3-phosphate O-acyltransferase of both potato and pea mitochondria used sn-glycerol-3-phosphate but not dihydroxyacetone phosphate as acyl acceptor and exclusively catalyzed the formation of 1-acyl-sn-glycerol-3-phosphate which subsequently served as substrate for the second acylation reaction at its C-2 position. Both acyltransferases of potato as well as pea mitochondria showed higher activities with acyl-CoA than with the corresponding acyl-(acyl carrier protein) thioesters. When different acyl-CoA thioesters were offered separately, the sn-glycerol-3-phosphate O-acyltransferase of potato mitochondria displayed no fatty acid specificity whereas the enzyme of pea mitochondria revealed one for saturated acyl groups. On the other hand, the mitochondrial 1-acyl-sn-glycerol-3-phosphate O-acyltransferases from both potato tubers and pea leaves were more active on unsaturated than on saturated acyl-CoA thioesters. Furthermore, these enzymes preferentially used oleoyl- and linoleoyl-CoA when they were offered in a mixture with saturated ones, although the fatty acid selectivity of the pea enzyme was less pronounced than that of the potato enzyme. The sn-glycerol-3-phosphate O-acyltransferase of potato mitochondria displayed a slight preference for saturated acyl groups.

1-Acylglycerol-3-Phosphate O-Acyltransferase↗

Artificial elevation of brain tissue glycerol by administration of a glycerol-containing agent. Case report.

In recent years the development of secondary brain damage and derangement of neurochemical parameters after severe head injury has been monitored using microdialysis. Provided the blood-brain barrier is intact, glycerol is regarded as a potential marker for membrane phospholipid degradation. The authors report a case in which marked elevation of interstitial glycerol was induced after exogenous administration of a glycerol-containing agent. A 25-year-old man was injured in a motorcycle accident and was admitted to the authors' institution with a unilateral dilated and fixed pupil and a Glasgow Coma Scale score of 3. Computerized tomography scans revealed a large subdural hematoma on the left side, subsequent midline shift, and generalized edema. Emergency craniotomy was performed for evacuation of the hematoma. The patient was prepared for multisensory monitoring and a microdialysis catheter was inserted into his left frontal lobe. After a routine enema containing 85% glycerol had been administered, the authors measured a marked increase in glycerol in the dialysate. This occurred while the patient was in as stable a condition as could be expected given the circumstances. The increase in interstitial glycerol in the injured tissue was most likely due to an impaired blood-brain barrier. Thus, the interstitial glycerol concentration had been corrupted by exogenous glycerol, and the marker properties of glycerol in this case became questionable. Consequently, administration of glycerol, which is frequently found in various infusions and emulsions, can promote secondary brain damage by adversely shifting osmotic gradients.

Adult↗

Determination of glycerol turnover by stable-isotope technique in humans: a new [1,1,2,3,3-2H5]glycerol derivative for mass-spectrometry analysis.

The stable isotope-labeled [1,1,2,3,3-2H5]glycerol analyzed by negative-ion chemical ionization (NCI) mass spectrometry has been proven a valid tracer for studying glycerol kinetics in humans. Because of its high technical complexity, NCI mass spectrometry is available to only a few laboratories. Thus, the aim of our study was to create an alternative method for measuring [1,1,2,3,3-2H5]glycerol enrichment in plasma with a new derivative and positive-ion chemical ionization (PCI) mass spectrometry. It could be demonstrated that the trisacetyl[1,1,2,3,3-2H5]glycerol derivative was able to produce a fragment at m/z = 164 with sufficient intensity. Application of [1,1,2,3,3-2H5]glycerol in seven healthy volunteers resulted in reproducible measurements of basal glycerol turnover rates. The mean glycerol flux rate of 3.02 +/- 0.37 mumol.kg-1 body wt.min-1 after an overnight fast was similar to values reported from studies with comparable protocols. Physiological changes of lipolysis rates after 48 h of fasting followed by infusion of 4 mg.kg-1 body wt.min-1 glucose could also be adequately studied in one subject. Fast-induced elevated glycerol turnover at 7.56 mumol.kg-1 body wt.min-1, was substantially suppressed to 1.13 mumol.kg-1 body wt.min-1, when glucose was administered. The easily performed trisacetyl[1,1,2,3,3-2H5]glycerol derivative analyzed by PCI mass spectrometry is suitable for studying glycerol kinetics in humans.

Acetic Anhydrides↗

Uptake and dissimilation of glycerol by wild type and glycerol nonutilizing strains of Neurospora crassa.

Seven mutant strains defective for utilization of glycerol, glyceraldehyde or dihydroxyacetone were isolated. One strain was deficient for NAD-linked glycerol-3-phosphate dehydrogenase, two for glycerol kinase, and four had no detected enzymatic deficiency, although one of the latter strains was deficient in glycerol uptake. Glycerol uptake was increased by incubation in glycerol, glycerol-3-phosphate, erythritol, and propanediol, and was protein-mediated below 0.14 mM glycerol, but at higher concentrations free diffusion predominated. Glycerol uptake was decreased by cycloheximide and was more sensitive to sodium azide than to iodoacetate.

Glycerol↗

Relationships in different parts of the nephron between enzymes of glycerol metabolism and the metabolite changes which result from large glycerol loads.

Glycerol metabolism in 9 defined parts of rat nephron was studied by measurement of glycerol kinase and observation of effects of large glycerol loads on related metabolites and on ATP and total adenylate. Glycerol kinase with glycerol as substrate was highest in the proximal convoluted tubule, slightly lower in straight portions, 20 to 25 times lower in distal segments, and almost indetectable elsewhere. With dihydroxyacetone as substrate, enzyme distribution differed little except for 30% lower activity in proximal convoluted segments. Methods of measurement with 10-40 ng of freeze-dried tissue are described. Glycerol loads produced large accumulations of glycerol 3-phosphate in proximal segments and in distal convoluted tubules. In the control nephron, fructose bisphosphate plus triose phosphates was 1 times higher in distal straight and convoluted segments than in proximal segments. Increases with glycerol loads were limited to proximal straight tubules (2-fold) and the thin limb area (60%). Glucose-6-P increased 3-fold in the late portion of the proximal straight tubule but not elsewhere. ATP and total adenylate were markedly depleted no phosphorylated intermediates accumulated. Levels of Pi were decreased in whole cortex and medullar following glycerol loads.

Adenine Nucleotides↗

Temporary reversal of serum to cerebrospinal fluid glycerol concentration gradient after intravenous infusion of glycerol.

Glycerol 50 g infused i.v. over 2 to 6 h is widely used to treat cerebral oedema in patients with acute stroke. Its transit through the blood-cerebrospinal fluid barrier in subjects with uninflamed meninges has now been examined. In 7 patients with an external ventriculostomy for occlusive hydrocephalus, each of whom was given 500 ml of a 10% solution IV over 4 h, serum and CSF were repeatedly sampled during and after the infusion and glycerol was measured enzymatically. The highest serum glycerol level of 191-923 mg/l was observed at the end of the infusion. The maximum CSF glycerol of 18.7-110.8 mg/l was attained 0-1 h after the end of the infusion. Elimination both from serum and CSF approximated a single-exponential decay; the elimination half-life from serum was 0.29-0.56 h compared to 1.03-3.68 h from CSF. In six of the seven cases there was a temporary reversal of the serum/CSF concentration gradient during glycerol elimination. The ratios of the AUCs of CSF and serum, which describe the overall penetration of glycerol into CSF, ranged from 0.09-0.31. In conclusion, the serum level of glycerol produced by giving 50 g IV glycerol over 4 h may not be sufficiently high reliably dehydrate to brain tissue in many patients, and the slow elimination of glycerol from the CSF may be related to the so-called rebound phenomenon.

Adult↗

Metabolism of [1,3-13C]glycerol-1,2,3-tris(methylsuccinate) and glycerol-1,2,3-tris(methyl[2,3-13C]succinate) in rat hepatocytes.

Hepatocytes prepared from overnight-fasted rats were incubated for 120 minutes in the presence of 2.5 mmol/L [1,3-13C]glycerol-1,2,3-tris(methylsuccinate) or glycerol-1,2,3-tris(methyl[2,3-13C]succinate). The identification and quantification of 13C-enriched metabolites by a recently developed method for the deconvolution of nuclear magnetic resonance (NMR) spectra with multiplet structures and constraints documented a virtually complete recovery of [1,3-13C]glycerol-1,2,3-tris(methylsuccinate) in 13C-labeled glycerol, lactic acid, and glucose. In hepatocytes exposed to [1,3-13C]glycerol-1,2,3-tris(methylsuccinate), glucose was symmetrically labeled, with the vast majority of hexose molecules being enriched with 13C on both C1 and C3 and/or C6 and C4. The respective abundance of glucose isotopomers labeled either on both C3 and C4 or on only 1 of these 2 C atoms indicated that the triose phosphates generated from [1,3-13C]glycerol represented 44% +/- 1% of the total amount of triose phosphates incorporated into the hexose. In hepatocytes exposed to glycerol-1,2,3-tris(methyl[2,3-13C]succinate), the recovery of [2,3-13C]succinate, [2,3-13C]fumarate, and either double- or single-labeled malate, lactate, alanine, and glucose accounted for about half the initial 13C content of the ester. The majority of the glucose molecules were now labeled in both C, and C2 or C6 and C5, with a preferential labeling of C6-C5 relative to C1-C2, the paired C6/C1 and C5/C2 ratios averaging 1.33 +/-0.04. These findings show that glycerol-1,2,3-tris(methylsuccinate) is efficiently and extensively metabolized in hepatocytes. They reinforce the concept that the asymmetry of glucose 13C-labeling by triose phosphates generated from Krebs cycle intermediates is modulated by the availability of glycerol-derived triose phosphates. Lastly, the present study indicates that the latter triose esters, under the present experimental conditions which do not aim at duplicating the physiological in vivo situation, are largely directly channelled in the gluconeogenic pathway, with only a limited intrahepatic contribution of the "indirect" pathway involving their back-and-forth interconversion to and from pyruvate.

Amino Acids↗

Heterologous expression of Zygosaccharomyces rouxii glycerol 3-phosphate dehydrogenase gene (ZrGPD1) and glycerol dehydrogenase gene (ZrGCY1) in Saccharomyces cerevisiae.

We examined the effects of heterologous expression of the open reading frames (ORF) of two genes on salt tolerance and glycerol production in a Saccharomyces cerevisiae strain deficient in glycerol synthesis (gpd1Deltagpd2Delta). When the ORF of the Zygosaccharomyces rouxii glycerol 3-phosphate dehydrogenase gene (ZrGPD1) was expressed under the control of the GAL10 promoter, salt tolerance and glycerol production increased; when the ORF of the glycerol dehydrogenase gene (ZrGCY1) was expressed under the control of the GAL1 promoter, no such changes were observed. Zrgcy1p had a weak effect on glycerol production. These results suggest that Zrgpd1p is the primary enzyme involved in Z. rouxii glycerol production, following a mechanism similar to that of S. cerevisiae (Gpd1p). When the ORFs of the S. cerevisiae glycerol 3-phosphatase gene (GPP2) and ZrGPD1 were simultaneously expressed, glycerol production increased, compared with that in yeast expressing only ZrGPD1.

Cloning, Molecular↗

Roles of glycerol and glycerol-3-phosphate dehydrogenase (NAD+) in acquired osmotolerance of Saccharomyces cerevisiae.

In a cell culture of Saccharomyces cerevisiae exponentially growing in basal medium, only 0.02% of the cells were osmotolerant, i.e., survived transfer to medium containing 1.4 M NaCl. Short-time conditioning in 0.7 M NaCl medium transformed the whole population into an osmotolerance phenotype. During this conditioning, the rate of formation of glycerol, the main compatible solute in S. cerevisiae, increased threefold and the specific activity of glycerol-3-phosphate dehydrogenase (NAD+) (GPDH) (EC 1.1.1.8) was enhanced sixfold. The apparent flux control coefficient for GPDH in the formation of glycerol was estimated to be 0.6. Glycerol production was also favored by regulated activities of alcohol dehydrogenase (EC 1.1.1.1) and aldehyde dehydrogenase [NAD(P)]+ (EC 1.2.1.5). About 50% of the total glycerol produced during conditioning in 0.7 M NaCl was retained intracellularly, and the increased glycerol accumulation was shown to be not merely a result of enhanced production rate but also of increased retention of glycerol. Washing the cells with solutions of lower salinities resulted in loss of glycerol, with retained levels proportional to the concentration of NaCl in the washing solution. Cycloheximide addition inhibited the development of acquired osmotolerance and conditioned cells washed free of glycerol retained a high degree of osmotolerance, which indicate that protein synthesis was required to establish the osmotolerance state.

Cycloheximide↗

GPD1, which encodes glycerol-3-phosphate dehydrogenase, is essential for growth under osmotic stress in Saccharomyces cerevisiae, and its expression is regulated by the high-osmolarity glycerol response pathway.

The yeast Saccharomyces cerevisiae responds to osmotic stress, i.e., an increase in osmolarity of the growth medium, by enhanced production and intracellular accumulation of glycerol as a compatible solute. We have cloned a gene encoding the key enzyme of glycerol synthesis, the NADH-dependent cytosolic glycerol-3-phosphate dehydrogenase, and we named it GPD1. gpd1 delta mutants produced very little glycerol, and they were sensitive to osmotic stress. Thus, glycerol production is indeed essential for the growth of yeast cells during reduced water availability. hog1 delta mutants lacking a protein kinase involved in osmostress-induced signal transduction (the high-osmolarity glycerol response [HOG] pathway) failed to increase glycerol-3-phosphate dehydrogenase activity and mRNA levels when osmotic stress was imposed. Thus, expression of GPD1 is regulated through the HOG pathway. However, there may be Hog1-independent mechanisms mediating osmostress-induced glycerol accumulation, since a hog1 delta strain could still enhance its glycerol content, although less than the wild type. hog1 delta mutants are more sensitive to osmotic stress than isogenic gpd1 delta strains, and gpd1 delta hog1 delta double mutants are even more sensitive than either single mutant. Thus, the HOG pathway most probably has additional targets in the mechanism of adaptation to hypertonic medium.

Amino Acid Sequence↗

Lipid transport in the human newborn. Palmitate and glycerol turnover and the contribution of glycerol to neonatal hepatic glucose output.

Free fatty acid (FFA) transport was measured in 11 and glycerol turnover in 5 newborns with continuous tracer infusion of [1-(13)C]palmitate or [2-(13)C]glycerol, respectively. In addition, simultaneous determination of glucose production in the latter group with [6,6-(2)H(2)]glucose tracer and measurement of the appearance rate of [(13)C]glucose derived from [(13)C]glycerol allowed calculation of gluconeogenesis from glycerol.The average FFA inflow rate was 11.5+/-1.7 mumol kg(-1)min(-1), 2.5-4.5 h after the last feeding, and 16.7+/-2.8 mumol kg(-1)min(-1), 5-12 h after the last meal. These rates are comparable to those found in adults only after 8-16 h and approximately 72 h of fasting, respectively. FFA inflow in the newborn was directly correlated with time of fasting, plasma FFA level, and plasma glycerol level. Palmitate clearance and fractional removal were inversely related to palmitate level. Glycerol flux averaged 4.4+/-0.5 mumol kg(-1)min(-1), a value three- to fourfold that of the postabsorptive adult. Approximately 75% of transported glycerol was converted to glucose and represented 5.0+/-0.6% of hepatic glucose production. Furthermore, there was a direct relationship between glycerol turnover and the fraction of glucose coming from glycerol. Despite the absolutely elevated neonatal FFA and glycerol transport rates, these were quantitatively similar to values found in adults with comparable elevated substrate levels. Furthermore, other similarities with the adult in the relationships between inflow transport and substrate values, and between transport and fractional removal suggest that the regulatory aspects of lipid transport in man are already well developed by the first day of life.

Blood Glucose↗