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

Radiolabeled pyruvate, glucose, glucose-6-phosphate, acetate, and malate are all variously utilized for fatty acid and glycerolipid biosynthesis by isolated pea (Pisum sativum L.) root plastids. At the highest concentrations tested (3-5mM), the rates of incorporation of these precursors into fatty acids were 183, 154, 125, 99 and 57 nmol h-1 mg-1 protein, respectively. In all cases, cold pyruvate consistently caused the greatest reduction, whereas cold acetate consistently caused the least reduction, in the amounts of each of the other radioactive precursors utilized for fatty acid biosynthesis. Acetate incorporation into fatty acids was approximately 55% dependent on exogenously supplied reduced nucleotides (NADH and NADPH), whereas the utilization of the remaining precursors was only approximately 10 and 20% dependent on added NAD(P)H. In contrast, the utilization of all precursors was greatly dependent (85-95%) on exogenously supplied ATP. Palmitate, stearate, and oleate were the only fatty acids synthesized from radioactive precursors. Higher concentrations of each precursor caused increased proportions of oleate and decreased proportions of palmitate synthesized. Radioactive fatty acids from all precursors were incorporated into glycerolipids. The data presented indicate that the entire pathway from glucose, including glycolysis, to fatty acids and glycerolipids is operating in pea root plastids. This pathway can supply both carbon and reduced nucleotides required for fatty acid biosynthesis but only a small portion of the ATP required
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PMID:The Utilization of Glycolytic Intermediates as Precursors for Fatty Acid Biosynthesis by Pea Root Plastids. 1222 67

The present study compares the exogenous NAD(P)H oxidation and the membrane potential ([delta][psi]) generated in mitochondria isolated from different tissues of an important agricultural crop, sugar beet (Beta vulgaris}. We observed that mitochondria from taproots, cold-stored taproots, and in vitro-grown tissue cultures contain a functional NADH dehydrogenase, whereas only those isolated from tissue cultures displayed a functional NAD(P)H dehydrogenase. It is interesting that the NADH-dependent [delta][psi] of mitochondria from cold-stored taproots and from tissue cultures was not affected by free Ca2+ ions, whereas free Ca2+ was required for the mitochondrial NADPH oxidation by in vitro-grown cells and cytosolic NADH oxidation by mitochondria from fresh taproots. A tentative model accounting for the different response to Ca2+ ions of the NADH dehydrogenase in mitochondria from cold-stored taproots and tissue cultures of B. vulgaris is discussed.
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PMID:Oxidation of External NAD(P)H by Mitochondria from Taproots and Tissue Cultures of Sugar Beet (Beta vulgaris). 1223 47

Vegetative buds of peach (Prunus persica L. Batsch.) trees act as strong sinks and their bud break capacity can be profoundly affected by carbohydrate availability during the rest period (November-February). Analysis of xylem sap revealed seasonal changes in concentrations of sorbitol and hexoses (glucose and fructose). Sorbitol concentrations decreased and hexose concentrations increased with increasing bud break capacity. Sucrose concentration in xylem sap increased significantly but remained low. To clarify their respective roles in the early events of bud break, carbohydrate concentrations and uptake rates, and activities of NAD-dependent sorbitol dehydrogenase (SDH), sorbitol oxidase (SOX) and cell wall invertase (CWI) were determined in meristematic tissues, cushion tissues and stem segments. Only CWI activity increased in meristematic tissues shortly before bud break. In buds displaying high bud break capacity (during January and February), concentrations of sorbitol and sucrose in meristematic tissues were almost unchanged, paralleling their low rates of uptake and utilization by meristematic tissues, and indicating that sorbitol and sucrose play a negligible role in the bud break process. Hexose concentrations in meristematic tissues and glucose imported by meristematic tissues correlated positively with bud break capacity, suggesting that hexoses are involved in the early events of bud break. These findings were confirmed by data for buds that were unable to break because they had been collected from trees deprived of cold. We therefore conclude that hexoses are of greater importance than sorbitol or sucrose in the early events of bud break in peach trees.
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PMID:Trophic control of bud break in peach (Prunus persica) trees: a possible role of hexoses. 1499 62

In green parts of the plant, during illumination ATP and NAD(P)H act as energy sources that are generated mainly in photosynthesis and respiration, whereas in darkness, glycolysis, respiration and the oxidative pentose-phosphate pathway (OPP) generate the required energy forms. In non-green parts, sugar oxidation in glycolysis, respiration and OPP are the only means of producing energy. For energy-consuming reactions, the delivery of NADPH, NADH, reduced ferredoxin and ATP has to take place at the required rates and in the specific compartments, since the pool sizes of these energy carriers are rather limited and, in general, they are not directly transported across biomembranes. Indirect transport of reducing equivalents can be achieved by malateoxaloacetate shuttles, involving malate dehydrogenase (MDH) for the interconversion. Isoenzymes of MDH are present in each cellular compartment. Chloroplasts contain the redox-controlled NADP-MDH that is only active in the light. In addition, a plastid NAD-MDH that is permanently active and is present in all plastid types has been found. Export of excess NAD(P)H through the malate valves will allow for the continued production of ATP (1) in photosynthesis, and (2) in oxidative phosphorylation. In the latter case, the coupled production of NADH is catalysed by the bispecific NAD(P)-GAPDH (GapAB) in chloroplasts that is active with NAD even in darkness, or by the specific plastid NAD-GAPDH (GapCp) in non-green tissues. When plants are subjected to conditions such as high light, high CO(2), NH(4) (+) nutrition, cold stress, which require changed activities of the enzymes of the malate valves, changed expression levels of the MDH isoforms can be observed. In nodules, the induction of a nodule-specific plastid NAD-MDH indicates the changed requirements for energy supply during N(2) fixation. Furthermore, the induction of glucose 6-phosphate dehydrogenase isoforms by ammonium and of ferredoxin and ferredoxin-NADP reductase by nitrate has been described. All these findings are in line with the assumption that a changed redox state caused by metabolic variability leads to the induction of enzymes involved in redox poise.
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PMID:Malate valves to balance cellular energy supply. 1503 73

The capacity to accumulate winter polyols (mainly ribitol and sorbitol) during cold-acclimation in Pyrrhocoris apterus is restricted only to the adults that have previously entered diapause. The enzymatic complement involved in polyol biosynthesis was found to differ in a complex manner between diapause and non-diapause adults. Nearly 100% of glycogen phosphorylase (GPase) was present in its active form in non-diapause adults irrespective of their acclimation status. In contrast, less than 40% of GPase was present in its active form in diapause adults prior to cold-acclimation and the inactive form was rapidly activated upon transition from 5 to 0 degrees C, concomitantly with the start of rapid polyol accumulation. The flow of carbon released by activation of glycogen degradation might be routed to the pentose cycle because the activity of glucose-6-P dehydrogenase (G(6)P-DH) was significantly higher and it increased with cold-acclimation in diapause adults while it was relatively low and it decreased with cold-acclimation in non-diapause adults. Reducing equivalents in the form of NADPH, which were generated in the pentose cycle, might require re-oxidation. Such re-oxidation might be achieved during reduction of sugars to polyols. The activity of NADP(H)-dependent aldose reductase (AR) was about 20-fold higher in diapause than in non-diapause adults. Similarly, the activity of NAD(H)-dependent polyol dehydrogenase (PDH) was higher in diapause adults. In addition, we found a very high activity of an unusual enzyme, NADP(H)-dependent ketose reductase (KR), exclusively in diapause adults. KR might be involved in reduction of fructose to sorbitol. Although its affinity for fructose as a substrate was low (K(M)=0.64M), its activity was about 10-fold higher than that of PDH with fructose. Moreover, the activity of KR significantly increased with cold-acclimation while that of PDH remained unchanged. Different electrophoretic mobilities in PAGE gel suggested that KR and PDH are two different enzymes with specific requirement for NADP(H) or NAD(H), respectively, as co-factors.
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PMID:Adjustments of the enzymatic complement for polyol biosynthesis and accumulation in diapausing cold-acclimated adults of Pyrrhocoris apterus. 1508 23

Microbacterium luteolum YK-1 has pyridoxine degradation pathway I. We have cloned the structural gene for the second step enzyme, pyridoxal 4-dehydrogenase. The gene consists of 1,026-bp nucleotides and encodes 342 amino acids. The enzyme was overexpressed under cold shock conditions with a coexpression system and chaperonin GroEL/ES. The recombinant enzyme showed the same properties as the M. luteolum enzyme. The primary sequence of the enzyme was 54% identical with that of d-threo-aldose 1-dehydrogenase from Agrobacterium tumefaciens, a probable aldo-keto reductase (AKR). Upon multiple alignment with enzymes belonging to the 14 AKR families so far reported, pyridoxal 4-dehydrogenase was found to form a new AKR superfamily (AKR15) together with A. tumefaciens d-threo-aldose 1-dehydrogenase and Pseudomonas sp. l-fucose dehydrogenase. These enzymes belong to a distinct branch from the two main ones found in the phylogenic tree of AKR proteins. The enzymes on the new branch are characterized by their inability to reduce the corresponding lactones, which are produced from pyridoxal or sugars. Furthermore, pyridoxal 4-dehydrogenase prefers NAD(+) to NADP(+) as a cofactor, although AKRs generally show higher affinities for the latter.
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PMID:Molecular cloning, expression, and properties of an unusual aldo-keto reductase family enzyme, pyridoxal 4-dehydrogenase, that catalyzes irreversible oxidation of pyridoxal. 1522 11

We have determined the underlying sites of H(2)O(2) generation by isolated rat brain mitochondria and how these can shift depending on the presence of respiratory substrates, electron transport chain modulators and exposure to stressors. H(2)O(2) production was determined using the fluorogenic Amplex red and peroxidase system. H(2)O(2) production was higher when succinate was used as a respiratory substrate than with another FAD-dependent substrate, alpha-glycerophosphate, or with the NAD-dependent substrates, glutamate/malate. Depolarization by the uncoupler p-trifluoromethoxyphenylhydrazone decreased H(2)O(2) production stimulated by all respiratory substrates. H(2)O(2) production supported by succinate during reverse transfer of electrons was decreased by inhibitors of complex I (rotenone and diphenyleneiodonium) whereas in glutamate/malate-oxidizing mitochondria diphenyleneiodonium decreased while rotenone increased H(2)O(2) generation. The complex III inhibitors antimycin and myxothiazol decreased succinate-induced H(2)O(2) production but stimulated H(2)O(2) production in glutamate/malate-oxidizing mitochondria. Antimycin and myxothiazol also increased H(2)O(2) production in mitochondria using alpha-glycerophosphate as a respiratory substrate. In substrate/inhibitor experiments maximal stimulation of H(2)O(2) production by complex I was observed with the alpha-glycerophosphate/antimycin combination. In addition, three forms of in vitro mitochondrial stress were studied: Ca(2+) overload, cold storage for more than 24 h and cytochrome c depletion. In each case we observed (i) a decrease in succinate-supported H(2)O(2) production by complex I and an increase in succinate-supported H(2)O(2) production by complex III, (ii) increased glutamate/malate-induced H(2)O(2) generation by complex I and (iii) increased alpha-glycerophosphate-supported H(2)O(2) generation by complex III. Our results suggest that all three forms of mitochondrial stress resulted in similar shifts in the localization of sites of H(2)O(2) generation and that, in both normal and stressed states, the level and location of H(2)O(2) production depend on the predominant energetic substrate.
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PMID:Shift in the localization of sites of hydrogen peroxide production in brain mitochondria by mitochondrial stress. 1522 97

A unique variant of glutathione independent formaldehyde dehydrogenase of Pseudomonas putida was obtained by random mutagenesis using the PCR-reaction. This YM042 mutant, S318G, was a cold-adapted formaldehyde dehyrogenase. The activity at 29 degrees C of the variant was 1.7-fold higher than that of the wild type. The K(m) values of the mutant at 37 degrees C were 0.40 mM for NAD(+) and 2.5 mM for formaldehyde, while those of the wild-type were 0.18 mM for NAD(+) and 2.1 mM for formaldehyde. The catalytic efficiency for formaldehyde was about 1.5-fold greater in the mutant than in the wild-type enzyme. The optimum pHs and temperatures of the mutant and the wild-type enzyme were 7.5, and 8.0 and 37 degrees C, and 47 degrees C, respectively. The thermal stability of the mutant was lower than that of the wild type.
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PMID:The artificial evolution of an enzyme by random mutagenesis: the development of formaldehyde dehydrogenase. 1532 56

The contribution of endogenous fluorophores - such as proteins, bound and free NAD(P)H, flavins, vitamin A, arachidonic acid - to the liver autofluorescence was studied on tissue homogenate extracts and on isolated hepatocytes by means of spectrofluorometric analysis. Autofluorescence spectral analysis was then applied to investigate the response of single living hepatocytes to experimental conditions resembling the various phases of the organ transplantation. The following conditions were considered: 1 h after cells isolation (reference condition); cold hypoxia; rewarming-reoxygenation after cold preservation. The main alterations occurred for NAD(P)H and flavins, the coenzymes strictly involved in energetic metabolism. During cold hypoxia NAD(P)H, mainly the bound form, showed an increase followed by a slow decrease, in agreement with the inability of the respiratory chain to reoxidize the coenzyme, and a subsequent NADH reoxidation through alternative anaerobic metabolic pathways. Both bound/free NAD(P)H and total NAD(P)H/flavin ratio values were altered during cold hypoxia, but approached the reference condition values after rewarming-reoxygenation, indicating the cells capability to restore the basal redox equilibrium. A decrease of arachidonic acid and vitamin A contributions occurred after cold hypoxia: in the former case it may depend on the balance between deacylation and reacylation of fatty acids, in the latter it might be related to the vitamin A antioxidant role. An influence of physico-chemical status and microenvironment on the fluorescence efficiency of these fluorophores cannot be excluded. In general, all the changes observed for cell autofluorescence properties were consistent with the complex metabolic pathways providing for energy supply.
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PMID:Autofluorescence properties of isolated rat hepatocytes under different metabolic conditions. 1548 Apr 82

Plant mitochondria differ from those of mammals, since they incorporate an alternative electron transport pathway, which branches at ubiquinol to an alternative oxidase (AOX), characteristically inhibited by salicylhydroxamic acid (SHAM). Another feature of plant mitochondria is that besides complex I (EC 1.6.5.3) they possess alternative NAD(P)H-dehydrogenases insensitive to rotenone. Many stress conditions are known to alter the expression of the alternative electron transport pathway in plant mitochondria. In the present study we investigated the effects of some thiol reagents and Ca(2+) on potato mitochondrial respiratory chain presenting different activities of the alternative respiratory components AOX and external NADH dehydrogenase, a condition induced by previous treatment of potato tubers (Solanum tuberosum L., cv. Bintje) to cold stress. The results showed that Ca(2+) presented an inhibitory effect on AOX pathway in potato mitochondria energized with NADH or succinate, which was only now observed when the cytochrome pathway was inhibited by cyanide. When the cytochrome pathway was functional, Ca(2+) stimulated the external NADH dehydrogenase. Diamide was a potent AOX inhibitor and this effect was only now observed when the cytochrome pathway was inactive, as was the case for the calcium ion. Mersalyl inhibited the externally located NADH dehydrogenase and had no effect on AOX activity. The results may represent an important function of Ca(2+) on the alternative mitochondrial enzymes NADH-DH(ext) and AOX.
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PMID:Sensitivities of the alternative respiratory components of potato tuber mitochondria to thiol reagents and Ca2+. 1576 67


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