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PubMed1988

Effects of glycerol concentration, equilibration time and temperature of glycerol addition on post-thaw viability of boar spermatozoa frozen in straws.

Experiments were conducted to study the effect of glycerol concentration, equilibration time and temperature of glycerol addition on post-thaw viability of boar spermatozoa after cryopreservation in straws. Semen (split ejaculate) in maxi-straws (6 mm o.d.) was frozen using a programmable freezing chamber. Three methods for in vitro sperm evaluation were used: motility (MOT), acrosome integrity (NAR) and flow cytometric analysis of sperm treated with carboxyfluorescein diacetate and propidium iodide to assess sperm plasma membrane integrity (PMI). No interactions were found among the three variables evaluated. Length of prefreeze exposure to glycerol, ranging from .5 min to 75 min, had no effect on post-thaw sperm viability. Exposure of sperm to a glycerol-containing extender medium at 5 degrees C gave improved post-thaw viability over that exposed at 0 degree C (P less than .05). Glycerol at a concentration of 3 or 4% resulted in maximum post-thaw MOT. Acrosome integrity values were greatest for 2 and 3% glycerol, whereas PMI was greatest when glycerol concentration was 4 to 6%. The primary cryoprotective effect of glycerol on boar semen may be extracellular. It is concluded that 3 or 4% glycerol gives maximum viability of frozen-thawed spermatozoa when the present methods are employed.

Acrosome↗
PubMed1980

Comparative utilization in vivo of [U-14C] glycerol, [2-3H] glycerol, [U-14C] glucose and [1-C14] palmitate in the rat.

Female rats were injected i.v. with comparable trace amounts of [U-14C] glycerol, [2-3H] glycerol, [U-14C] glucose, or [1-14C] palmitate, and killed 30 min afterwards. The radioactivity remaining in plasma at that time was maximal in animals receiving [U-14C] glucose while the appearance of radioactive lipids was higher in the [U-14C] glycerol animals than in other groups receiving hydrosoluble substrates. The carcass, more than the liver, was the tissue where the greatest proportion of radioactivity was recovered, while the greatest percentage of radioactivity appeared in the liver in the form of lipids. The values of total radioactivity found in different tissues were very similar when using either labelled glucose or glycerol but the amount recovered as lipids was much greater in the latter. The maximal proportion of radioactive lipids appeared in the fatty-acid form in the liver, carcass, and lumbar fat pads when using [U-14C] glycerol as a hydrosoluble substrate, and the highest lipidic fraction appeared in adipose tissue as labelled, esterified fatty acids. In the spleen, heart, and kidney, most of the lipidic radioactivity from any of the hydrosoluble substrates appeared as glyceride glycerol. The highest proportion of radioactivity from [1-14C] palmitate appeared in the esterified fatty acid in adipose tissue, being followed in decreasing proportion by the heart, carcass, liver, kidney, and spleen. Thus at least in part, both labelled glucose and glycerol are used throughout different routes for their conversion in vivo to lipids. A certain proportion of glycerol is directly utilized by adipose tissue. The fatty acids esterification ability differs among the tissues and does not correspond directly with the reported activities of glycerokinase, suggesting that the alpha-glycerophosphate for esterification comes mainly from glucose and not from glycerol.

Animals↗
PubMed1998

Measurement of plasma glycerol specific activity by high performance liquid chromatography to determine glycerol flux.

Previous methods for measuring plasma glycerol specific activity (SA) are suboptimal, making the determination of glycerol kinetics in vivo with radiotracers difficult. A new high performance liquid chromatography (HPLC) method is described that permits the accurate and specific measurement of glycerol SA. The method involves isolation of glycerol from plasma and the formation of a tribenzoyl derivative. Glycerol rate of appearance was measured in five human volunteers using both [2-3H]glycerol and [2H5] glycerol. There was close agreement between the glycerol appearance rates measured using the two approaches (1.66 +/- 0.14 vs. 1.70 +/- 0.10 micromol x kg(-1) x min(-1), respectively, P = NS). This HPLC method offers improved specificity over existing methods of measuring glycerol turnover using radiotracers.

Chromatography, High Pressure Liquid↗
PubMed1991

Osmoregulation in Saccharomyces cerevisiae. Studies on the osmotic induction of glycerol production and glycerol-3-phosphate dehydrogenase (NAD+)

Production of glycerol and a key enzyme in glycerol production, glycerol 3-phosphate dehydrogenase (NAD+) (GPD), was studied in Saccharomyces cerevisiae cultured in basal media or media of high salinity, with glucose, raffinose or ethanol as the sole carbon source. At high salinity, glycerol production was stimulated with all carbon sources and glycerol was accumulated to high intracellular concentration in cells grown on glucose and raffinose. Cells grown on ethanol accumulated glycerol to a lower level but showed an increased content of trehalose at high salinity. However, the trehalose concentration corresponded only to about 20% of the glycerol level, and did not compensate for the shortfall in intracellular osmolyte content. Immunoblot analysis demonstrated an increased production of GPD at high salinity. This increase was osmotically mediated but was lower when glycerol was substituted for NaCl or sorbitol as the stress-solute. The enzyme also appeared to be subject to glucose repression; the specific activity of GPD was significantly lower in cells grown on glucose, than on raffinose or ethanol.

Ethanol↗
PubMed1993

Regulation of glycerol metabolism in Enterococcus faecalis by phosphoenolpyruvate-dependent phosphorylation of glycerol kinase catalyzed by enzyme I and HPr of the phosphotransferase system.

Using a polyclonal antibody against glycerol kinase from Enterococcus faecalis, we could demonstrate that glycerol kinase is inducible by growth on glycerol-containing medium and that during growth on glycerol the enzyme is mainly phosphorylated. Glucose and other sugars metabolized via the Embden-Meyerhof pathway strongly repressed the synthesis of glycerol kinase, while if glycerol was also present during growth, low activity, reflecting partial induction and the presence of mainly unphosphorylated, less active enzyme, was found. With gluconate, which is also a substrate of the phosphotransferase system, repression of glycerol kinase was less severe, but the enzyme was mainly present in the less active, unphosphorylated form. Effects of growth on different carbon sources on glycerol uptake are also reported.

Bacterial Proteins↗
PubMed1996

A single amino acid change in Escherichia coli glycerol kinase abolishes glucose control of glycerol utilization in vivo.

Escherichia coli glycerol kinase (EC 2.7.1.30; ATP:glycerol 3-phosphotransferase) is a key element in glucose control of glycerol metabolism. Its catalytic activity is inhibited allosterically by the glycolytic intermediate, fructose 1,6-biphosphate, and by the phosphotransferase system phosphocarrier protein, IIIGlc (also known as IIAGlc). These inhibitors provide mechanisms by which glucose blocks glycerol utilization in vivo. We report here the cloning and sequencing of the glpK22 gene isolated from E. C. C. Lin strain 43, a strain that shows the loss of glucose control of glycerol utilization. DNA sequencing shows a single missense mutation that translates to the amino acid change Gly-304 to Ser (G-304-S) in glycerol kinase. The effects of this substitution on the functional and physical properties of the purified mutant enzyme were determined. Neither of the allosteric ligands inhibits it under conditions that produce strong inhibition of the wild-type enzyme, which is sufficient to explain the phenotype of strain 43. However, IIIGlc activates the mutant enzyme, which could not be predicted from the phenotype. In the wild-type enzyme, G-304 is located 1.3 nm from the active site and 2.5 nm from the IIIGlc binding site (M. Feese, D. W. Pettigrew, N. D. Meadow, S. Roseman, and S. J. Remington, Proc. Natl. Acad. Sci. USA 91:3544-3548, 1994). It is located in the same region as amino acid substitutions in the related protein DnaK which alter its catalytic and regulatory properties and which are postulated to interfere with a domain closure motion (A. S. Kamath-Loeb, C. Z. Lu, W.-C. Suh, M. A. Lonetto, and C. A. Gross, J. Biol. Chem. 270:30051-30059, 1995). The global effect of the G-304-S substitution on the conformation and catalytic and regulatory properties of glycerol kinase is consistent with a role for the domain closure motion in the molecular mechanism for glucose control of glycerol utilization.

Allosteric Regulation↗
PubMed2004

Glycerol metabolism of Lactobacillus rhamnosus ATCC 7469: cloning and expression of two glycerol kinase genes.

Lactobacillus rhamnosus ATCC 7469 was able to grow in glycerol as the sole source of energy in aerobic conditions, producing lactate, acetate, and diacetyl. A biphasic growth was observed in the presence of glucose. In this condition, glycerol consumption began after glucose was exhausted from the culture medium. Glycerol kinase activity was detected in L. rhamnosus ATCC 7469, a characteristic of microorganisms which catabolize glycerol in aerobic conditions. Genetic analysis revealed that this strain possesses two glycerol kinase genes: gykA and glpK, that encode for two different glycerol kinases GykA and GlpK, respectively. The glpK geneis associated in an operon with alpha-glycerophosphate oxidase (glpO) and glycerol facilitator (glpF) genes. Transcriptional analysis revealed that only glpK is expressed when L. rhamnosus was grown on glycerol.

Acetates↗
PubMed1985

Glycerol kinase deficiency inhibits glycerol utilization in phosphoglyceride and triacylglycerol biosynthesis.

Glycerol 3-phosphate is an initial metabolite in the biosynthesis of phosphoglycerides and triacylglycerols. Both glycerol and glucose are precursors of glycerol 3-phosphate. Cultured skin fibroblasts from patients with glycerol kinase deficiency utilized glucose, but not glycerol in the biosynthesis of phosphoglycerides and triacylglycerols. Phosphoglyceride and triacylglycerol biosynthesis in glycerol kinase deficiency fibroblasts is not diminished by the inability to use glycerol as a precursor of glycerol 3-phosphate.

Cells, Cultured↗
PubMed1996

Reduced pyruvate decarboxylase and increased glycerol-3-phosphate dehydrogenase [NAD+] levels enhance glycerol production in Saccharomyces cerevisiae.

This investigation deals with factors affecting the production of glycerol in Saccharomyces cerevisiae. In particular, the impact of reduced pyruvate-decarboxylase (PDC) and increased NAD-dependent glycerol-3-phosphate dehydrogenase (GPD) levels was studied. The glycerol yield was 4.7 times (a pdc mutant exhibiting 19% of normal PDC activity) and 6.5 times (a strain exhibiting 20-fold increased GPD activity resulting from overexpression of GPD1 gene) that of the wild type. In the strain carrying both enzyme activity alterations, the glycerol yield was 8.1 times higher than that of the wild type. In all cases, the substantial increase in glycerol yield was associated with a reduction in ethanol yield and a higher by-product formation. The rate of glycerol formation in the pdc mutant was, due to a slower rate of glucose catabolism, only twice that of the wild type, and was increased by GPD1 overexpression to three times that of the wild-type level. Overexpression of GPD1 in the wild-type background, however, led to a six- to seven-fold increase in the rate of glycerol formation. The experimental work clearly demonstrates the rate-limiting role of GPD in glycerol formation in S. cerevisiae.

Adenosine Triphosphate↗
PubMed1997

Modulation of glycerol and ethanol yields during alcoholic fermentation in Saccharomyces cerevisiae strains overexpressed or disrupted for GPD1 encoding glycerol 3-phosphate dehydrogenase.

The possibility of the diversion of carbon flux from ethanol towards glycerol in Saccharomyces cerevisiae during alcoholic fermentation was investigated. Variations in the glycerol 3-phosphate dehydrogenase (GPDH) level and similar trends for alcohol dehydrogenase (ADH), pyruvate decarboxylase and glycerol-3-phosphatase were found when low and high glycerol-forming wine yeast strains were compared. GPDH is thus a limiting enzyme for glycerol production. Wine yeast strains with modulated GPD1 (encoding one of the two GPDH isoenzymes) expression were constructed and characterized during fermentation on glucose-rich medium. Engineered strains fermented glucose with a strongly modified [glycerol] : [ethanol] ratio. gpd1delta mutants exhibited a 50% decrease in glycerol production and increased ethanol yield. Overexpression of GPD1 on synthetic must (200 g/l glucose) resulted in a substantial increase in glycerol production ( x 4) at the expense of ethanol. Acetaldehyde accumulated through the competitive regeneration of NADH via GPDH. Accumulation of by-products such as pyruvate, acetate, acetoin, 2,3 butane-diol and succinate was observed, with a marked increase in acetoin production.

Base Sequence↗
PubMed1993

[Glycerol as feed component and 14C-glycerol metabolism in rats].

Male Wistar rats (initial weight 58 g) received in four groups (10 animals per group) 0.0, 10.6, 21.3, and 31.8% glycerol in the dry matter of the diet (groups 1 to 4). The live weight gain of the animals was, after a feeding time of 3 weeks in the groups 1 to 4, 2.01, 2.49, 2.57, and 2.52 g, respectively, per animal and day. The higher gain in the glycerol groups resulted from the higher feed intake in these groups. Four rats per group received on the 22nd day of the experiment, 1 h after the morning meal, an intraperitoneal injection of carrier-free 14C-glycerol. The 14C-excretion in the respiration air and in the urine was measured in the following 10 h. The 14C-excretion in the 14CO2 of the respiration air was in % of the injected 14C-glycerol doses in the groups 1 to 4 = 45.4, 44.2, 39.0, and 33.2, respectively. The 14C-excretion in the urine was 17.0, 18.1, 25.1, and 32.3%, respectively. The higher values in groups 3 and 4 resulted from the high excretion of free glycerol in the urine. In groups 3 and 4 the glycerol content of the blood plasma was 1.9- and 1.5-fold higher than in groups 1 and 2. It was concluded that up to 40 mg glycerol per hour and animal (100 gLW) was metabolized in a physiological way in group 2. As a feeding component glycerol can constitute up to 10% of the diet-DM in monogastric animals.

Animal Feed↗
PubMed2004

The fungal STRE-element-binding protein Seb1 is involved but not essential for glycerol dehydrogenase (gld1) gene expression and glycerol accumulation in Trichoderma atroviride during osmotic stress.

Fungi counteract extracellular osmotic pressure by producing intracellular polyols to prevent loss of water. In yeast osmotic signaling involves a MAP-kinase pathway culminating at the STRE-binding transcription factors Msn2/4. We investigated the role of a putative STRE-binding orthologue of Trichoderma atroviride, Seb1, in osmotic stress signaling. T. atroviride, subjected to osmotic stress (10% glucose or glycerol, 1M KCl or NaCl), responds by raising its intracellular glycerol level. In contrast to Aspergillus nidulans, no erythritol is accumulated. Accumulation of glycerol levels under osmotic stress is strongly reduced in a seb1 deletion strain. To investigate glycerol biosynthesis in T. atroviride, the genes encoding glycerol dehydrogenase (gld1) and glycerol-3-phosphate dehydrogenase (gfd1) were cloned and characterized. Although both genes contain STRE-elements in their 5'-non-coding regions, only gld1 mRNA accumulates in response to osmotic stress, whereas expression of gfd1 remains at a constitutive level. In comparison to A. nidulans gld1 transcript levels in T. atroviride rise very slowly under conditions of salt stress. Deletion of seb1 results in a delayed accumulation of the gld1 transcript, but final levels match those in the wild-type whereas gfd1 transcript accumulation remains unaffected. Assays for glycerol dehydrogenase and glycerol-3-phosphate dehydrogenase enzymatic activities reveal an increase of the former--whereas the latter remains mainly unaffected--in the wild-type and the Deltaseb1 strain under different kinds of osmotic stress. The data suggest that Seb1 is only involved in, but not essential for osmotic stress response which is in contrast to the yeast orthologues Msn2/4.

5' Untranslated Regions↗
PubMed2003

Glycerol conductance and physical asymmetry of the Escherichia coli glycerol facilitator GlpF.

The aquaglyceroporin GlpF is a transmembrane channel of Escherichia coli that facilitates the uptake of glycerol by the cell. Its high glycerol uptake rate is crucial for the cell to survive in very low glycerol concentrations. Although GlpF allows both influx and outflux of glycerol, its structure, similar to the structure of maltoporin, exhibits a significant degree of asymmetry. The potential of mean force characterizing glycerol in the channel shows a corresponding asymmetry with an attractive vestibule only at the periplasmic side. In this study, we analyze the potential of mean force, showing that a simplified six-step model captures the kinetics and yields a glycerol conduction rate that agrees well with observation. The vestibule improves the conduction rate by 40% and 75% at 10- micro M and 10-mM periplasmic glycerol concentrations, respectively. In addition, neither the conduction rate nor the conduction probability for a single glycerol (efficiency) depends on the orientation of GlpF. GlpF appears to conduct equally well in both directions under physiological conditions.

Aquaporins↗
PubMed2002

Comparison of liver enzymes in osmerid fishes: key differences between a glycerol accumulating species, rainbow smelt (Osmerus mordax), and a species that does not accumulate glycerol, capelin (Mallotus villosus).

Activities of enzymes associated with glycerol synthesis were compared in the liver of two osmerid fishes, the smelt (Osmerus mordax), which can accumulate high (400 mM) levels of glycerol and capelin (Mallotus villosus) that does not accumulate glycerol. Animals were sampled at approximately the same time of year and temperature thus negating potential seasonal effects. These species are closely related, reducing interpretative issues involving comparison between unrelated species. We found that key enzyme activities were elevated in the smelt relative to the non-glycerol accumulating capelin, namely enzymes involved with glycolysis (phosphofructose kinase-1 and aldolase), amino acid metabolism (aspartate aminotransferase and alanine aminotransferase), gluconeogenesis (phosphoenolpyruvate carboxykinase) and glycerol synthesis (glycerol-3-phosphate dehydrogenase). The enzyme profiles strongly support the hypothesis that smelt can synthesize glycerol by utilizing glycogen and amino acids as the carbon source and that they have increased capacity for metabolic flux through loci required for synthesis of the three carbon intermediate dihydroxyacetone phosphate and subsequently glycerol synthesis.

Amino Acids↗
PubMed1982

Glycerol fermentation in Klebsiella pneumoniae: functions of the coenzyme B12-dependent glycerol and diol dehydratases.

Glycerol and diol dehydratases are inducible, coenzyme B12-dependent enzymes found together in Klebsiella pneumoniae ATCC 25955 during anaerobic growth on glycerol. Mutants of this strain isolated by a novel procedure were separately constitutive for either dehydratase, showing the structural genes for the two enzymes to be under independent control in vivo. Glycerol dehydratase and a trimethylene glycol dehydrogenase were implicated as members of a pleiotropic control system that includes glycerol dehydrogenase and dihydroxyacetone kinase for the anaerobic dissimilation of glycerol (the "dha system"). The dehydratase and dehydrogenases were induced by dihydroxyacetone and were jointly constitutive in mutants isolated as constitutive for either the dha system or glycerol dehydratase. These data and the stimulation of growth by Co2+ suggested that glycerol dehydratase and trimethylene glycol dehydrogenase are obligatory enzymes for anaerobic growth on glycerol as the sole carbon source.

Alcohol Oxidoreductases↗
PubMed1974

Incorporation of (2-3H)glycerol into rat brain 1,2-diacyl-sn-glycero-3-phosphorylcholine and 1,2-diacyl-sn-glycerol molecular species in vivo.

Rat brain 1,2-diacyl-sn-glycerols (diglycerides) and 1,2-diacyl-sn-glycerols obtained from 1,2-diacyl-sn-glycero-3-phosphorylcholine after treatment with phospholipase C differ markedly in carbon number distribution. 70% of the 1,2-diacyl-sn-glycerols had a total of 38 fatty acid carbon atoms, and there was no detectable change in the 1,2-diacyl-sn-glycerol mass pattern between 7 and 23 days of age. In contrast, 1,2-diacyl-sn-glycero-3-phosphorylcholine contained at most 10% of this molecular species in the brains of rats of comparable age. A small increase in the C(36) species of 1,2-diacyl-sn-glycero-3-phosphorylcholine, which is associated with myelination, was noted between 10 and 17 days. The incorporation of intracranially injected [2-(3)H]glycerol into 1,2-diacyl-sn-glycero-3-phosphoryl-choline species with polyunsaturated fatty acids containing 20 or 22 carbon atoms was greater than into the species containing only saturated and/or monoenoic fatty acids between 30 min and 24 hr. The 1,2-diacyl-sn-glycerol fractions containing polyunsaturated fatty acids had the lowest specific activity at 30 min. The specific activity of the particular 1,2-diacyl-sn-glycerol fraction containing the stearate-arachidonate pair is the lowest for 4 hr after intracranial injection of the isotope. Thus, molecular species of 1,2-diacyl-sn-glycerol and 1,2-diacyl-sn-glycero-3-phosphorylcholine differed considerably in their labeling patterns, and a direct precursor-product relationship could not be demonstrated during the time period studied.

Animals↗