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141.
Abstract. In the preliminary purification of Capsicum leaf nitrate reductase (EC 1.6.6.1), treatment of the crude extract on Sephadex G-25 was necessary to prevent a gelling of the extract and sedimentation of the enzyme. Its Km values for NADH and nitrate were estimated to be 9.3 and 105mmol m−3 ADP and ATP gave hyperbolic competitive inhibition, with respect to NADH, while the inhibition by AMP was linear competitive. Ki values calculated were: ADP and ATP approximately lmol m−3 and AMP 2.3 mol m−3 . Inhibition by ADP was not altered by reduced glutathione.
The Capsicum nitrate reduclase was very susceptible to inhibition by NADH (in the absence of nitrate) and an in vivo assay showed that the activity of the enzyme was limited by the supply of nitrate. NADH and adenine nucleotide levels measured in the Capsicum leaf were used to estimate inhibition of nitrate reductase and a prediction was made of the nitrate reductase activity at different times in the photoperiod. This was shown to follow the same trend as the measured in vivo activity of the enzyme. Changes in adenine nucleotide levels had little effect on nitrate reductase activity. 相似文献
The Capsicum nitrate reduclase was very susceptible to inhibition by NADH (in the absence of nitrate) and an in vivo assay showed that the activity of the enzyme was limited by the supply of nitrate. NADH and adenine nucleotide levels measured in the Capsicum leaf were used to estimate inhibition of nitrate reductase and a prediction was made of the nitrate reductase activity at different times in the photoperiod. This was shown to follow the same trend as the measured in vivo activity of the enzyme. Changes in adenine nucleotide levels had little effect on nitrate reductase activity. 相似文献
142.
Samples of neocortex removed at diagnostic craniotomy from patients with Alzheimer's disease and incubated in vitro showed an increased production of 14CO2 from [U-14C]glucose compared with neurosurgical controls. This was a feature of incubations in the presence of both 5 mM K+ (142% control) and 31 mM K+ (126%). Specific labelling of the amino acid pool was unaltered, suggesting that the apparent increase of CO2 production was not merely a reflection of changes in dilution of the radiolabel from glucose. The content of adenine nucleotides was significantly less than control values in the tissue from patients with Alzheimer's disease after in vitro incubations but the adenylate energy charge was unchanged, indicating that normal energy metabolism was not grossly impaired in these preparations. 相似文献
143.
Effect of Inorganic Lead on Rat Brain Mitochondrial Respiration and Energy Production 总被引:2,自引:1,他引:1
Debra E. Gmerek Mary R. McCafferty Kevin J. O'Neill Brian R. Melamed John J. O'Neill 《Journal of neurochemistry》1981,36(3):1109-1113
Abstract: Toxicologically significant amounts of inorganic lead were added to rat brain mitochondrial preparations that did not contain EDTA or Pi . The binding of the lead to the mitochondria was measured by anodic stripping voltometry. In the presence of lead, the respiratory control ratios decreased, implying a decrease in the degree of dependence of respiration on a phosphate acceptor. Nucleotide contents were also measured, and in the presence of inorganic lead the actual amounts of ATP formed from ADP were found to be significantly decreased as well. 相似文献
144.
Patric A. Clapshaw Hans Werner Müller Wilfried Seifert 《Journal of neurochemistry》1981,36(6):1996-2003
The enzyme 2':3'-cyclic nucleotide 3'-phosphodiesterase (CNPase) was isolated from bovine brain white matter by a rapid (72 h) procedure. The minimum molecular weight (MW) of the enzyme was approximately 52,500 as estimated by sucrose density gradient analysis. When this isolated enzyme was stimulated with bovine serum albumin (BSA), the peak of activity was shifted to approximately 90,000 MW. Prior treatment by trypsin blocked the expression of the higher MW form of CNPase, but not the BSA activation of the enzyme. If the trypsin digestion was allowed to progress, the MW was gradually lowered to a broad peak sedimenting between 20,000 and 50,000 MW. An apparently soluble form of CNPase found in serum is described. Kinetic and MW comparisons between the serum soluble enzyme and CNPase isolated from bovine brain, as well as an analysis of substrate specificity, were made and it was concluded that the two enzymes were identical. 相似文献
145.
The reduction of ferric leghemoglobin (Lb3+) from soybean (Glycine max (L.) Merr.) nodules by riboflavin, FMN and FAD in the presence of NAD(P)H was studied in vitro. The system NAD(P)H + flavin reduced Lb3+ to oxyferrous (Lb2+ · O2) or deoxyferrous (Lb2+) leghemoglobin in aerobic or anaerobic conditions, respectively. In the absence of O2 the reaction was faster and more effective (i.e. less NAD(P)H oxidized per mole Lb3+ reduced) than in the presence of O2; this phenomenon was probably because O2 competes with Lb3+ for reductant, thus generating activated O2 species. The flavin-mediated reduction of Lb3+ did not entail production of superoxide or peroxide, indicating that NAD(P)H-reduced flavins were able to reduce Lb3+ directly. The NAD(P)H + flavin system also reduced the complexes Lb3+ · nicotinate and Lb3+ · acetate to Lb2+ · O2, Lb2+ or Lb2+ · nicotinate, depending on the concentrations of ligands and of O2. In the presence of 200 M nitrite most Lb remained as Lb3+ in aerobic conditions but the nitrosyl complex (Lb2+ · NO) was generated in anaerobic conditions. The above-mentioned characteristics of the NAD(P)H + flavin system, coupled with its effectiveness in reducing Lb3+ at physiological levels of NAD(P)H and flavins in soybean nodules, indicate that this mechanism may be especially important for reducing Lb3+ in vivo.Abbreviations and Terminology FLbR
ferric leghemoglobin reductase
- Hb2+ /Hb3+
hemoglobin containing Fe2+ /Fe2+
- Lb2+ /Lb3+
leghemoglobin containing Fe2+ /Fe3+
- Lb3+ · nicotinate/acetate
Lb in which nicotinate or acetate are complexed to Lb3+
- Lb2+ · O2/CO/NO/nicotinate
Lb in which O2, CO, NO or nicotinate are complexed to Lb2+
- Rfl
riboflavin
- SOD
superoxide dismutase (EC 1.15.1.1)
Published as Paper No. 9237, Journal Series, Nebraska Agricultural Research DivisionWe thank M.B. Crusellas for his skillful drawings. M. Becana thanks the Spanish Ministry of Education and Science/Fulbright Commission for financial support. 相似文献
146.
The inhibitory effects of botulinum neurotoxins types A and B on Ca2(+)-dependent evoked release of [3H]noradrenaline from rat cerebrocortical synaptosomes were compared and their molecular basis investigated. A23187, a Ca2+ ionophore, proved more efficacious in reversing the blockade produced by type A than that by B, whereas the actions of neither were changed by increasing intraterminal cyclic GMP levels using 8-bromo-cyclic GMP of nitroprusside. Disruption of the actin-based cytoskeleton with cytochalasin D did not alter the inhibition seen subsequently with either toxin. However, prior disassembly of microtubules with colchicine, nocodazole, or griseofulvin reduced the potency of type B toxin, but not that of type A toxin; stabilization of the microtubules with taxol counteracted this effect of colchicine. Because colchicine treatment of synaptosomes did not interfere with the measurable binding of type B toxin or its apparent uptake, it appears to act intracellularly. Collectively, these data suggest that botulinum neurotoxins types A and B inactivate transmitter release by interaction at different sites in the process. Based on the consistent results observed with four different drugs known to affect selectively microtubules, their involvement in the action of the type B neurotoxin is proposed. 相似文献
147.
148.
Differences and Similarities in Muscarinic Receptors of Rat Heart and Retina: Effects of Agonists, Guanine Nucleotides, and N-Ethylmaleimide 总被引:5,自引:4,他引:1
Muscarinic receptor stimulation inhibits cyclic AMP formation in rat atria but not in retina. We compared the properties of the muscarinic receptors in rat atrial and retinal membranes using the antagonist [3H]quinuclidinyl benzilate. In both atria and retina there is a single binding site for antagonists, while agonists appear to interact at two classes of binding sites. Muscarinic receptors in atria and retina have the same apparent affinities for several antagonists and for a series of muscarinic agonists. In both tissues N-ethylmaleimide decreases agonist affinity for the high-affinity binding sites. Muscarinic receptors in atria and retina differ, however, in several properties relating to the proportions of high- and low-affinity agonist sites. First, guanine nucleotides markedly increase the proportion of low-affinity binding sites in atria, but not in retina. Second, for all agonists there are fewer high-affinity binding sites in retina. Third, the "partial agonist" pilocarpine appears to interact with two classes of binding sites in atria, but with only a single class of sites in retina. Our data suggest that muscarinic receptors that inhibit cyclic AMP formation and those that do not share common properties that determine receptor affinity for agonists and classic antagonists. The differences between these receptors are manifest, however, in the effects of guanine nucleotides and the ability of agonists, especially those of low efficacy, to affect the proportion of high- and low-affinity sites and to effect a biological response. 相似文献
149.
The protective effect of ADP on unspecific Ca2+ release and collapse of the transmembrane potential was analyzed in mitochondria from kidneys of rats. The presence of ADP in the incubation mixture prevents Ca2+ leakage and collapse of in sucrose-containing medium, but fails to do so in KCl medium. The effect of the adenine nucleotide in sucrose media correlates with an increase in the level of reduced pyridine nucleotides; the increase was due to a stimulatory effect on the activity of glutamic dehydrogenase. It also was observed that in KCl media, in the presence and in the absence of ADP the rate of NADH oxidation through the respiratory chain was higher than in sucrose; in this latter medium a high level of reduced pyridine nucleotides was found, in comparison to KCl media. It is proposed that the role of ADP is to increase glutamic dehydrogenase activity and in consequence to provoke a higher rate of formation of NADH which in turn controls Ca2+ release. 相似文献
150.
It has been reported earlier that nucleotides, nucleosides and a series of structurally related compounds as well as compounds
based on transition state analogy inhibit yeast glyoxalase I. In our study on the metabolic regulation of glyoxalase I, we
have found that nucleotides such as ATP, GTP and different classes of other reagents based on transition state analogy (D-isoascorbate,
dihydroxyfumaric acid, rhodizonic acid) do not inhibit yeast or goat liver glyoxalase I. The reported inhibition of glyoxalase
I by these compounds has been found to be due to the interference of these compounds with the absorbancy at 240 nm of S-D-lactoylglutathione
formed by the glyoxalase I reaction.
Glyoxalase I from goat liver has been found to be strongly and competitively inhibited by lactaldehyde. But, lactaldehyde
has very little inhibitory effect on yeast glyoxalase I. Lactaldehyde is formed from methylglyoxal, the substrate for glyoxalase
I by the enzyme methylglyoxal reductase. D-Lactaldehyde inhibits the liver enzyme more strongly than L-lactaldehyde. 相似文献