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Query: UMLS:C0009443 (cold)
 92,137 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A partially purified soluble ATPase (ATP phosphohydrolase, EC 3.6.1.3) from pea cotyledon mitochondria was characterized. Inhibition patterns with azide, NaF, and cold, and a stimulation by 2,4-dinitrophenol were typical of F1-ATPases from mammalian mitochondria. The enzyme hydrolysed GTP, ITP, and ATP, but not CTP, UTP, ADP, or IDP. ATPase and ITPase activities were strongly inhibited by ADP and to a lesser extent by IDP. Distinctive properties of the pea mitochondrial enzyme were activation by high concentrations of CaCl2 and stimulation by NaCl.
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PMID:Partial characterization of a soluble ATPase from pea cotyledon mitochondria. 14 76

A temperature-dependent conformational change of the active DPN-linked isocitrate dehydrogenase was observed. When initial reaction kinetic data were examined between 35 and 5 degrees, the Hill number (n) varied from 2 at higher to n approaching unity at lower temperatures, with an inflection point at 17 degrees. The presence of manganous isocitrate in the incubation media shifted the transition temperature for enzyme inactivation by 5,5'-dithiobis(2-nitrobenzoate) from 8-16 degrees. These temperature-dependent transitions were paralleled by progressive changes in sedimentation velocities from s20, w of 10.4 at 25 degrees to 7.3 at 10 degrees as measured by active band centrifugation. The linear Arrhenius plot for apparent V max and the constancy of S0.5 for the substrate manganous isocitrate between 35 and 5 degrees suggest that this temperature-dependent conformational change may not be solely related to manganous isocitrate. Further indications of equilibria between different species of enzyme in solution and effects of substrates and cofactors on conformation came from studies of specific activity of enzyme diluted into buffers at 3 and 25 degrees. Dilution to concentrations between 10 and 25 mum enzyme resulted in relatively rapid protein concentration-dependent inactivation which could be prevented and fully reversed by manganous isocitrate. No further substantial inactivation was found subsequent to this phase at 25 degrees. Lowering the temperature of the dilution buffer to 3 degrees favored formation of enzyme species exhibiting a further time and pH-dependent loss of activity which became independent of protein concentration below 7 mum enzyme. The rate of cold inactivation was reduced by raising the ionic strength of the buffer and its progress could be arrested by manganous isocitrate; however, the substrate did not restore the original activity.
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PMID:Effects of temperature on diphosphopyridine nucleotide-linked isocitrate dehydrogenase from bovine heart. Aspects of the kinetics, stability, and quarternary structure of the enzyme. 23 54

Acclimation of carp both to the temperature fall (from 20 to 5 degrees C) and rise (from 20 to 30 degrees C) induces an increase in activity of cytoplasmic liver NADPH-generating enzymes--glucose-6-phosphate dehydrogenase (G6PDG) and malic-enzyme (ME) 6-phosphogluconate dehydrogenase (6PGDG) and NADP-isocitrate dehydrogenase (NADP-IDG) activities are unchanged. Actinomycin D does not prevent cold activation of G6PDG but blocks activation of ME. "Warm" G6PDG has minimal Km value for glucose-6-phosphate and "warm" ME has minimal Km value for glucose-6-phosphate and "warm" ME has minimal Km value for malate at 25 degrees C "Cold" G6PDG and ME have the warmest Km values at 5 degrees C. Isozyme composition of cytoplasmic G6PDG (2 bands with Rf 0.16 and 0.20) does not change within the limits of 5-30 degrees C. The prolactin action on G6PDG and ME is similar to the effect of cold acclimation (activity increases Km value decreases, isozyme pattern (for G6PDG) remains unchanged). It is supposed that activation of G6PDG and ME during cold adaptation may be a result of the prolactin action on substrate-binding ability without changes in the enzyme biosynthesis and isozyme pattern.
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PMID:[The effect of temperature acclimation on NADP-dependent dehydrogenase activity in the carp liver and various mechanisms of its regulation]. 323 95

Glutathione (GSH), together with NADPH-producing pathways and glutathione reductase, provides a defense system against oxidants. Oxidation of GSH causes stimulation of the hexose monophosphate shunt and increased production of NADPH. We have asked if hexose monophosphate shunt activity is required for the recovery of GSH following exposure of the isolated rat retina to an oxidant. Hexose monophosphate shunt activity was decreased by depleting the retina of hexose stores, before exposing the tissue to diamide (0.04-1.0mM), an oxidant for GSH, for 30 min. After exposure, retinas were transferred to either glucose-containing or glucose-free recovery medium for an additional 30 min. Control retinas kept in glucose-free, oxygenated medium (no diamide) for 90-120 min maintained GSH at 90% of the value found in retinas incubated with glucose. After exposure of hexose-depleted retinas to 0.4 mM diamide, a nearly 90% decrease in GSH was observed. When the oxidant was removed, the level of GSH returned to more than 80% of the control value in the presence or absence of glucose. In contrast, no recovery of GSH was observed after diamide treatment if the retinas were transferred to ice-cold (1-5 degrees C) media with or without glucose or if the retinas were pre-treated with 2 mM 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) to inhibit glutathione reductase. Measurements of two NADPH-producing cytosolic enzymes, namely NADP+-dependent malic enzyme and NADP+-dependent isocitrate dehydrogenase, revealed high activities. Optimum production of NADPH from malic enzyme was 0.90 nmol NADPH produced min-1 per retina, while with isocitrate dehydrogenase the average rate was 6.9 nmol NADPH produced min-1 per retina. We suggest that these enzymes together with a long-lived endogenous substrate (probably glutamate) are responsible for the recovery of GSH in hexose-depleted retinas. The present results suggest that more than one NADPH-producing system is capable of controlling the GSH concentration in retina. Studies that have focused on the hexose monophosphate shunt pathway as the sole source of NADPH for glutathione reductase in retina and other tissues may require re-evaluation depending on the overall metabolic capacity and substrate utilization of the particular tissue. Thus, the present findings are significant not only with respect to the retina but also for other tissues whose metabolic characteristics are similar to those found in the retina.
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PMID:Multiple NADPH-producing pathways control glutathione (GSH) content in retina. 380 64

1. The kinetics of the thermally induced enzyme variants of the supernatant NADP-isocitrate dehydrogenase from rainbow-trout liver are investigated. 2. Fish acclimatized to 2 degrees C (cold-adapted enzyme) and 17 degrees C (warm-adapted enzyme) show different relative distributions of the three NADP-isocitrate dehydrogenase isoenzymes; this has been demonstrated with electrophoresis and electrofocusing techniques. 3. Plots of K(m) versus temperature for the cold-adapted and warm-adapted enzyme variants are complex in nature with apparent maximal enzyme-substrate affinity corresponding to the temperature at which the trout is acclimatized. Both substrates, dl-isocitrate and NADP(+), give similar curves although the magnitude of the K(m) change with temperature is much decreased in the case of NADP(+). 4. E(a) values of approx. 18kcal/mol were determined for both the cold-adapted and warm-adapted enzyme variants. 5. In an attempt to determine how velocities can be increased at low temperatures, cation, pH requirements, metabolite and enzyme concentrations were examined. 6. NAD-isocitrate dehydrogenase could not be detected in trout tissues.
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PMID:Temperature and enzyme activity in poikilotherms. Isocitrate dehydrogenases in rainbow-trout liver. 439 98

Transcriptional control of the low-temperature-inducible icdII gene, encoding the thermolabile isocitrate dehydrogenase of a psychrophilic bacterium, Vibrio sp. strain ABE-1, was found to be mediated in part by a transcriptional silencer locating at nucleotide positions -560 to -526 upstream from the transcription start site of icdII. Deletion of the silencer resulted in a 20-fold-increased level of expression of the gene at low temperature (15 degrees C) but not at high temperature (37 degrees C). In addition, a CCAAT sequence located 2 bases upstream of the -35 region was found to be essential for the low-temperature-inducible expression of the gene. By deletion of this sequence, low-temperature-dependent expression of the gene was completely abolished. The ability of the icdII promoter to control the expression of other genes was confirmed by using a fusion gene containing the icdII promoter region and the promoterless icdI open reading frame, which encodes the non-cold-inducible isocitrate dehydrogenase isozyme of Vibrio sp. strain ABE-1. Escherichia coli transformants harboring icdII acquired an ability to grow rapidly at low temperature.
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PMID:cis-Acting elements responsible for low-temperature-inducible expression of the gene coding for the thermolabile isocitrate dehydrogenase isozyme of a psychrophilic bacterium, Vibrio sp. strain ABE-1. 1019 27

We found that a cold acclimation protein from an ice-nucleating bacterium, Patoea ananas KUIN-3, has refolding activity on frozen denatured protein. Based on a SDS-PAGE analysis, we confirmed that the cold shock-treated cells of strain KUIN-3 could produce some cold acclimation proteins that inhibit their syntheses by the addition of chloramphenicol during the cold acclimation. Among such proteins, Hsc25 had refolding activity similar to GroELS. Hsc25 was purified to apparent homogeneity by (NH4)2SO4 precipitation and some chromatographies. The purified Hsc25 was composed of 8 subunits of 25,000 each with a molecular mass of 200,000 and had refolding activity against denatured enzymes, which were denatured by heat-treatment at 100 degrees C, cryopreservation at -20 degrees C, or guanidine hydrochloride, in a manner similar to GroELS. The N-terminal sequence of Hsc25 was Met-Arg-Ala-Ser-Thr-Tyr-His-Ala-Ala-Arg-. Furthermore, Hsc25 had a high level of activity at low temperature (12 degrees C). Also, the dissociation constants, KD (M) as the binding specificity for enolase, mutarotase, isocitrate dehydrogenase, and lactate dehydrogenase were 1.82x10(-10), 4.35x10(-9), 8.98x10(-12), and 3.05x10(-11), respectively. The affinity of Hsc25 for frozen danatured enzymes was higher than the affinity for heat denatured enzymes when compared with the affinity of GroEL. These results are the first report on the characterization of a purified chaperon that was induced by cold acclimation.
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PMID:A cold acclimation protein with refolding activity on frozen denatured enzymes. 1121 Jan 32

The ice-nucleating bacterium, Pantoea agglomerans IFO12686, induces the cryoprotective protein (CRP) by cold acclimation at 12 degrees C. The CRP was purified to apparent homogeneity by various chromatographies. We found that the purified CRP was a monomer of approximately 29,000 according to gel filtration chromatography and SDS-PAGE, and was a heat-stable protein. The CRP could protect freeze-labile enzymes, lactate dehydrogenase (LDH), alcohol dehydrogenase (ADH) and isocitrate dehydrogenase (iCDH), against freezing-thawing denaturation. The activity of the CRP was about 3.5 x 10(4) times more effective than bovine serum albumin (BSA) and 2 x 10(6) times than COR26 from the ice-nucleating bacterium Pseudomonas fluorescens KUIN-1. We confirmed that the CRP was a novel protein, as judged by the a different molecule mass from the already-known cryoprotectants, and has an extremely high cryoprotective activity.
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PMID:A novel cryoprotective protein (CRP) with high activity from the ice-nucleating bacterium, Pantoea agglomerans IFO12686. 1138 69

Rapid changes in climate may impose strong selective pressures on organisms. Evolutionary responses to climate change have been observed in natural populations, yet no example has been documented for a metabolic enzyme locus. Furthermore, few studies have linked physiological responses to stress with allozyme genotypic variation. We quantified changes in allele frequency between 1988 and 1996 at three allozyme loci (isocitrate dehydrogenase, Idh; phosphoglucose isomerase, Pgi; and phosphoglucomutase, Pgm) for the leaf beetle Chrysomela aeneicollis in the Bishop Creek region of the Sierra Nevada of California (2900-3300 m). Beetles often experience high daytime (> 32 degrees C) and extremely low nighttime (< -5 degrees C) temperatures during summer. Bishop Creek weather station data indicated that conditions were unusually dry before 1988, and that conditions were cool and wet during the years preceding the 1996 collection. We found directional changes in allele frequency at Pgi (11% increase in the Pgi-1 allele), but not at Idh or Pgm. We also found that physiological response to thermal extremes depended on Pgi genotype. Pgi 1-1 individuals induced expression of a 70-kD heat shock protein (HSP) at lower temperatures than 1-4 or 4-4 individuals, and 1-1 individuals expressed higher levels of HSP70 after laboratory exposure to temperatures routinely experienced in nature. Survival after nighttime laboratory exposure to subzero temperatures depended on gender, previous exposure to cold, and Pgi genotype. Females expressed higher levels of HSP70 than males after exposure to heat, and recovery by female Pgi 1-1 homozygotes after exposure to cold (-5 degrees C) was significantly better than 1-4 or 4-4 genotypes. These data suggest that the cooler climate of the mid-1990s may have caused an increase in frequency of the Pgi-1 allele, due to a more robust physiological response to cold by Pgi 1-1 and 1-4 genotypes.
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PMID:Allele frequency shifts in response to climate change and physiological consequences of allozyme variation in a montane insect. 1248 57

Several properties of chimeric enzymes between a mesophilic isocitrate dehydrogenase (IDH) from a nitrogen-fixing bacterium, Azotobacter vinelandii, and a cold-adapted IDH isozyme (IDH-II) from a psychrophilic bacterium, Colwellia maris, were examined. Each of the genes encoding the IDHs was divided into four regions of almost equal lengths, and each region was ligated with different combinations to construct various chimeric genes. The resultant wild-type and chimeric genes were overexpressed in Escherichia coli. The wild-type and chimeric IDHs were classified into three groups based on optimum temperatures for activity of 20 degrees, 30 degrees, and 40 degrees C. The IDHs with a lower optimum temperature were more thermolabile. The optimum temperature and thermostability of the chimeric enzymes decreased on increasing the proportion derived from the cold-adapted IDH-II of C. maris. Furthermore, the C-terminal region of the C. maris IDH-II was suggested to be responsible for its psychrophilic characteristics.
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PMID:Characterization of chimeric isocitrate dehydrogenases of a mesophilic nitrogen-fixing bacterium, Azotobacter vinelandii, and a psychrophilic bacterium, Colwellia maris. 1506 Jul 37


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