(1/4138) Acute renal failure caused by nephrotoxins.
Renal micropuncture studies have greatly changed our views on the pathophysiology of acute renal failure caused by nephrotoxins. Formerly, this type of renal insufficiency was attributed to a direct effect of the nephrotoxins on tubule epithelial permeability. According to that theory, glomerular filtration was not greatly diminished, the filtrate formed being absorbed almost quantitatively and nonselectively across damaged tubule epithelium. Studies in a wide variety of rat models have now shown glomerular filtration to be reduced to a level which will inevitably cause renal failure in and of itself. Passive backflow of filtrate across tubular epithelium is either of minor degree or nonexistent even in models where frank tubular necrosis has occurred. This failure of filtration cannot be attributed to tubular obstruction since proximal tubule pressure is distinctly subnormal in most models studied. Instead, filtration failure appears best attributed to intrarenal hemodynamic alterations. While certain facts tend to incriminate the renin-angiotensin system as the cause of the hemodynamic aberrations, others argue to the contrary. The issue is underactive investigation. (+info)
(2/4138) Dietary control of triglyceride and phospholipid synthesis in rat liver slices.
1. The effect of dietary manipulation on the synthesis of triglycerides and phospholipids was investigated by determining the incorporation of labeled long-chain fatty acid or glycerol into these lipids in liver slices derived from normally fed, fasted, and fat-free refed rats. 2. Triglyceride synthesis was affected markedly by the dietary regime of the animal; the lowest rates were measured with fasted rats, and the highest ones with fat-free refed rats. 3. In contrast to triglyceride synthesis, phospholipid synthesis occured at virtually constant rates regardless of the dietary conditions. 4. Addition of large amounts of fatty acid to the incubation mixture resulted in a marked stimulation of triglyceride synthesis, whereas phospholipid synthesis was affected to a much smaller extent. 5. These results indicate that the synthesis of triglycerides and that of phospholipids are controlled independently, and that the availability of fatty acid in the cell contributes to the control of triglyceride synthesis. (+info)
(3/4138) Improved antibody detection by the use of range expansion and longer filter wavelength in a low ionic strength-protamine sulphate Auto-Analyzer system.
Range expansion, achieved by insertion of a variable resistance between the colorimeter and the recorder together with the use of 550 nm colorimeter filters, has resulted in markedly improved sensitivity for antibody detection, and improved sample identification, in a low ionic strength-protamine sulphate (LISPS) system. Range expansion also permits a lower concentration of red cells to be used, thus economizing on fully typed cells. Glycerol stored frozen cells were found to be only slightly less sensitive than fresh cells in this system. (+info)
(4/4138) Isocitrate lyase of Ashbya gossypii--transcriptional regulation and peroxisomal localization.
The isocitrate lyase-encoding gene AgICL1 from the filamentous hemiascomycete Ashbya gossypii was isolated by heterologous complementation of a Saccharomyces cerevisiae icl1d mutant. The open reading frame of 1680 bp encoded a protein of 560 amino acids with a calculated molecular weight of 62584. Disruption of the AgICL1 gene led to complete loss of AgIcl1p activity and inability to grow on oleic acid as sole carbon source. Compartmentation of AgIcl1p in peroxisomes was demonstrated both by Percoll density gradient centrifugation and by immunogold labeling of ultrathin sections using specific antibodies. This fitted with the peroxisomal targeting signal AKL predicted from the C-terminal DNA sequence. Northern blot analysis with mycelium grown on different carbon sources as well as AgICL1 promoter replacement with the constitutive AgTEF promoter revealed a regulation at the transcriptional level. AgICL1 was subject to glucose repression, derepressed by glycerol, partially induced by the C2 compounds ethanol and acetate, and fully induced by soybean oil. (+info)
(5/4138) Redundant systems of phosphatidic acid biosynthesis via acylation of glycerol-3-phosphate or dihydroxyacetone phosphate in the yeast Saccharomyces cerevisiae.
In the yeast Saccharomyces cerevisiae lipid particles harbor two acyltransferases, Gat1p and Slc1p, which catalyze subsequent steps of acylation required for the formation of phosphatidic acid. Both enzymes are also components of the endoplasmic reticulum, but this compartment contains additional acyltransferase(s) involved in the biosynthesis of phosphatidic acid (K. Athenstaedt and G. Daum, J. Bacteriol. 179:7611-7616, 1997). Using the gat1 mutant strain TTA1, we show here that Gat1p present in both subcellular fractions accepts glycerol-3-phosphate and dihydroxyacetone phosphate as a substrate. Similarly, the additional acyltransferase(s) present in the endoplasmic reticulum can acylate both precursors. In contrast, yeast mitochondria harbor an enzyme(s) that significantly prefers dihydroxyacetone phosphate as a substrate for acylation, suggesting that at least one additional independent acyltransferase is present in this organelle. Surprisingly, enzymatic activity of 1-acyldihydroxyacetone phosphate reductase, which is required for the conversion of 1-acyldihydroxyacetone phosphate to 1-acylglycerol-3-phosphate (lysophosphatidic acid), is detectable only in lipid particles and the endoplasmic reticulum and not in mitochondria. In vivo labeling of wild-type cells with [2-3H, U-14C]glycerol revealed that both glycerol-3-phosphate and dihydroxyacetone phosphate can be incorporated as a backbone of glycerolipids. In the gat1 mutant and the 1-acylglycerol-3-phosphate acyltransferase slc1 mutant, the dihydroxyacetone phosphate pathway of phosphatidic acid biosynthesis is slightly preferred as compared to the wild type. Thus, mutations of the major acyltransferases Gat1p and Slc1p lead to an increased contribution of mitochondrial acyltransferase(s) to glycerolipid synthesis due to their substrate preference for dihydroxyacetone phosphate. (+info)
(6/4138) The PalkBFGHJKL promoter is under carbon catabolite repression control in Pseudomonas oleovorans but not in Escherichia coli alk+ recombinants.
The alk genes are located on the OCT plasmid of Pseudomonas oleovorans and encode an inducible pathway for the utilization of n-alkanes as carbon and energy sources. We have investigated the influence of alternative carbon sources on the induction of this pathway in P. oleovorans and Escherichia coli alk+ recombinants. In doing so, we confirmed earlier reports that induction of alkane hydroxylase activity in pseudomonads is subject to carbon catabolite repression. Specifically, synthesis of the monooxygenase component AlkB is repressed at the transcriptional level. The alk genes have been cloned into plasmid pGEc47, which has a copy number of about 5 to 10 per cell in both E. coli and pseudomonads. Pseudomonas putida GPo12 is a P. oleovorans derivative cured of the OCT plasmid. Upon introduction of pGEc47 in this strain, carbon catabolite repression of alkane hydroxylase activity was reduced significantly. In cultures of recombinant E. coli HB101 and W3110 carrying pGEc47, induction of AlkB and transcription of the alkB gene were no longer subject to carbon catabolite repression. This suggests that carbon catabolite repression of alkane degradation is regulated differently in Pseudomonas and in E. coli strains. These results also indicate that PalkBFGHJKL, the Palk promoter, might be useful in attaining high expression levels of heterologous genes in E. coli grown on inexpensive carbon sources which normally trigger carbon catabolite repression of native expression systems in this host. (+info)
(7/4138) Characterization of the exopolygalacturonate lyase PelX of Erwinia chrysanthemi 3937.
Erwinia chrysanthemi 3937 secretes several pectinolytic enzymes, among which eight isoenzymes of pectate lyases with an endo-cleaving mode (PelA, PelB, PelC, PelD, PelE, PelI, PelL, and PelZ) have been identified. Two exo-cleaving enzymes, the exopolygalacturonate lyase, PelX, and an exo-poly-alpha-D-galacturonosidase, PehX, have been previously identified in other E. chrysanthemi strains. Using a genomic bank of a 3937 mutant with the major pel genes deleted, we cloned a pectinase gene identified as pelX, encoding the exopolygalacturonate lyase. The deduced amino acid sequence of the 3937 PelX is very similar to the PelX of another E. chrysanthemi strain, EC16, except in the 43 C-terminal amino acids. PelX also has homology to the endo-pectate lyase PelL of E. chrysanthemi but has a N-terminal extension of 324 residues. The transcription of pelX, analyzed by gene fusions, is dependent on several environmental conditions. It is induced by pectic catabolic products and affected by growth phase, oxygen limitation, nitrogen starvation, and catabolite repression. Regulation of pelX expression is dependent on the KdgR repressor, which controls almost all the steps of pectin catabolism, and on the global activator of sugar catabolism, cyclic AMP receptor protein. In contrast, PecS and PecT, two repressors of the transcription of most pectate lyase genes, are not involved in pelX expression. The pelX mutant displayed reduced pathogenicity on chicory leaves, but its virulence on potato tubers or Saintpaulia ionantha plants did not appear to be affected. The purified PelX protein has no maceration activity on plant tissues. Tetragalacturonate is the best substrate of PelX, but PelX also has good activity on longer oligomers. Therefore, the estimated number of binding subsites for PelX is 4, extending from subsites -2 to +2. PelX and PehX were shown to be localized in the periplasm of E. chrysanthemi 3937. PelX catalyzed the formation of unsaturated digalacturonates by attack from the reducing end of the substrate, while PehX released digalacturonates by attack from the nonreducing end of the substrate. Thus, the two types of exo-degrading enzymes appeared complementary in the degradation of pectic polymers, since they act on both extremities of the polymeric chain. (+info)
(8/4138) Glucose kinetics during prolonged exercise in highly trained human subjects: effect of glucose ingestion.
1. The objectives of this study were (1) to investigate whether glucose ingestion during prolonged exercise reduces whole body muscle glycogen oxidation, (2) to determine the extent to which glucose disappearing from the plasma is oxidized during exercise with and without carbohydrate ingestion and (3) to obtain an estimate of gluconeogenesis. 2. After an overnight fast, six well-trained cyclists exercised on three occasions for 120 min on a bicycle ergometer at 50 % maximum velocity of O2 uptake and ingested either water (Fast), or a 4 % glucose solution (Lo-Glu) or a 22 % glucose solution (Hi-Glu) during exercise. 3. Dual tracer infusion of [U-13C]-glucose and [6,6-2H2]-glucose was given to measure the rate of appearance (Ra) of glucose, muscle glycogen oxidation, glucose carbon recycling, metabolic clearance rate (MCR) and non-oxidative disposal of glucose. 4. Glucose ingestion markedly increased total Ra especially with Hi-Glu. After 120 min Ra and rate of disappearance (Rd) of glucose were 51-52 micromol kg-1 min-1 during Fast, 73-74 micromol kg-1 min-1 during Lo-Glu and 117-119 micromol kg-1 min-1 during Hi-Glu. The percentage of Rd oxidized was between 96 and 100 % in all trials. 5. Glycogen oxidation during exercise was not reduced by glucose ingestion. The vast majority of glucose disappearing from the plasma is oxidized and MCR increased markedly with glucose ingestion. Glucose carbon recycling was minimal suggesting that gluconeogenesis in these conditions is negligible. (+info)