scholarly journals The isocitrate dehydrogenases of Acinetobacter lwoffi. Studies on the regulation of nicotinamide–adenine dinucleotide phosphate-linked isoenzyme

1973 ◽  
Vol 132 (2) ◽  
pp. 215-221 ◽  
Author(s):  
Colin H. Self ◽  
Malcolm G. Parker ◽  
P. David J. Weitzman
Keyword(s):  
Molecular Weight ◽  
Nicotinamide Adenine Dinucleotide ◽  
Nicotinamide Adenine Dinucleotide Phosphate ◽  
Nicotinamide Adenine ◽  
Ph Optimum ◽  
Low Concentrations ◽  
Molecular Weight Form ◽  
Metabolic Significance ◽  
Regulatory Sites ◽  
Stimulation Of

Of the two NADP-linked isocitrate dehydrogenases in Acinetobacter lwoffi the higher-molecular-weight form, isoenzyme-II, is reversibly stimulated sixfold by low concentrations of glyoxylate or pyruvate. Kinetic results indicate that this stimulation of activity involves both an increase in Vmax. and a decrease in the apparent Km values for substrates, most markedly that for NADP+. Other changes brought about by glyoxylate or pyruvate include a shift in the pH optimum for activity and an increased stability to inactivation by heat or urea. Mixtures of glyoxylate plus oxaloacetate, known to inhibit isocitrate dehydrogenases from other organisms, produce inhibition of both A. lowffi isoenzymes, and do not reflect the stimulatory specificity of glyoxylate for isoenzyme-II. Isoenzyme-II is also stimulated by AMP and ADP, but the activation by glyoxylate or pyruvate is shown to be quite independent of the adenylate activation. Differential desensitization of the enzyme by urea to the two types of activator further supports the view that the enzyme possesses two distinct allosteric regulatory sites. The metabolic significance of the activations is discussed.

A disulfide reductase in spores of Bacillus cereus T

1971 ◽  
Vol 17 (10) ◽  
pp. 1273-1277 ◽  
Author(s):  
Leroy C. Blankenship ◽  
J. R. Mencher
Keyword(s):  
Molecular Weight ◽  
Bacillus Cereus ◽  
Nicotinamide Adenine Dinucleotide ◽  
Nicotinamide Adenine Dinucleotide Phosphate ◽  
Nicotinamide Adenine ◽  
Small Molecular Weight ◽  
Ph Optimum ◽  
Nitrobenzoic Acid ◽  
Disulfide Reductase ◽  
Reduced Nicotinamide Adenine Dinucleotide

An enzyme obtained from Bacillus cereus T spores which catalyzes the reduction of the disulfide, 5, 5′-dithiobis (2-nitrobenzoic acid) (DTNB), has been partially purified and characterized. The enzyme required either reduced nicotinamide adenine dinucleotide phosphate (NADPH2) or reduced nicotinamide adenine dinucleotide (NADH2) as electron donor. It had a pH optimum of 8, was destroyed by heating at 70C for 5 min, and was stimulated by Ca2+ and Mg2+. No other small molecular weight disulfides were found to be substrates for the enzyme.

scholarly journals The isocitrate dehydrogenases of Acinetobacter lwoffi. Separation and properties of two nicotinamide–adenine dinucleotide phosphate-linked isoenzymes

1972 ◽  
Vol 130 (1) ◽  
pp. 211-219 ◽  
Author(s):  
Colin H. Self ◽  
P. David J. Weitzman
Keyword(s):  
Molecular Weight ◽  
Ph Dependence ◽  
Gel Filtration ◽  
Deae Cellulose ◽  
Nicotinamide Adenine Dinucleotide Phosphate ◽  
Molecular Size ◽  
Ion Exchange Chromatography ◽  
Exchange Chromatography ◽  
Low Concentrations ◽  
Stimulation Of

Two isoenzymes of NADP-linked isocitrate dehydrogenase have been identified in Acinetobacter lwoffi and have been termed isoenzyme-I and isoenzyme-II. The isoenzymes may be separated by ion-exchange chromatography on DEAE-cellulose, by gel filtration on Sephadex G-200, or by zonal ultracentrifugation in a sucrose gradient. Low concentrations of glyoxylate or pyruvate effect considerable stimulation of the activity of isoenzyme-II. The isoenzymes also differ in pH-dependence of activity, kinetic parameters, stability to heat or urea and molecular size. Whereas isoenzyme-I resembles the NADP-linked isocitrate dehydrogenases from other organisms in having a molecular weight under 100000, isoenzyme-II is a much larger enzyme (molecular weight around 300000) resembling the NAD-linked isocitrate dehydrogenases of higher organisms.

scholarly journals Incorporation of L-[1-14C]leucine into protein by liver postmitochondrial supernatant: opposing effects of preincubated nicotinamide-adenine dinucleotide phosphate and 4-dimethylamino-3′-methylazobenzene

1975 ◽  
Vol 146 (2) ◽  
pp. 505-507 ◽  
Author(s):  
N P Madsen ◽  
J E Labuc
Keyword(s):  
Nicotinamide Adenine Dinucleotide ◽  
Nicotinamide Adenine Dinucleotide Phosphate ◽  
Nicotinamide Adenine ◽  
Free Protein ◽  
A Cell ◽  
Opposing Effects ◽  
Stimulation Of

Combination of preincubated drug-metabolizing medium containing NADP+ with a cell-free protein-synthesizing system resulted in marked stimulation of incorporation of L-[1-14C]leucine into protein. Addition of 4-dimethylamino-3′-methylazobenzene, present and previously preincubated in the drug-metabolizing medium, decreased this effect.

scholarly journals The effect of pH on the characteristics of the binding of nicotinamide–adenine dinucleotide by nicotinamide–adenine dinucleotide specific isocitrate dehydrogenase from pea mitochondria

1970 ◽  
Vol 116 (5) ◽  
pp. 819-824 ◽  
Author(s):  
G. F. Cox ◽  
D. D. Davies
Keyword(s):  
Isocitrate Dehydrogenase ◽  
Nicotinamide Adenine Dinucleotide ◽  
Maximum Velocity ◽  
Nicotinamide Adenine ◽  
Half Maximum ◽  
Ph Optimum ◽  
Effect Of Ph ◽  
Ph Values ◽  
Metabolic Significance

1. The effect of pH on the Vmax. and concentration of NAD+ at half-maximum velocity at a constant isocitrate concentration was examined, and the results were related to the requirements for binding of H+ ions to the enzyme. 2. The effect of varying the NAD+ concentration on the pH optimum with constant isocitrate concentration was studied. 3. A comparison has been made between the effect of isocitrate concentration on the characteristics of binding of NAD+ and the effect of NAD+ concentration on the characteristics of isocitrate binding at three different pH values. 4. The mechanistic and metabolic significance of these studies is considered.

EFFECTS OF LUTEINIZING HORMONE AND NICOTINAMIDE ADENINE DINUCLEOTIDE PHOSPHATE ON SYNTHESIS OF PROGESTATIONAL STEROIDS BY RABBIT OVARIAN TISSUE IN VITRO

1966 ◽  
Vol 35 (1) ◽  
pp. 65-73 ◽  
Author(s):  
J. H. DORRINGTON ◽  
R. KILPATRICK
Keyword(s):  
Luteinizing Hormone ◽  
Nicotinamide Adenine Dinucleotide ◽  
Ovarian Tissue ◽  
Nicotinamide Adenine Dinucleotide Phosphate ◽  
Nicotinamide Adenine ◽  
Steroid Synthesis ◽  
Activity Measurements ◽  
Progesterone Synthesis ◽  
Stimulation Of

SUMMARY Luteinizing hormone (LH) stimulated synthesis of both progesterone and 20α-hydroxypregn-4-en-3-one by rabbit ovarian tissue in vitro. Progesterone synthesis was stimulated by nicotinamide adenine dinucleotide phosphate (NADP), but 20α-hydroxypregn-4-en-3-one production was only slightly affected by NADP compared with the effect of LH. When NADP was added with glucose-6-phosphate (G-6-P) or 6-phospho-gluconate (6-P-G), no apparent stimulation of progestational steroid synthesis occurred. Specific activity measurements suggested that stimulation of synthesis was masked by increased conversion of progestational steroids to other products. When NADP and submaximal concentrations of LH were used together, potentiation rather than addition of effects on progesterone synthesis was found, and addition of effects with supramaximal concentrations of LH. No potentiation was found when NADP was replaced by NADP and G-6-P or 6-P-G, or by NADPH2. NADP, unlike LH, caused striking stimulation of progesterone synthesis by separated corpora lutea. It is suggested that the present results provide further support for the view that the actions of LH and NADP are related.

scholarly journals The effects of pH and citrate on the activity of nicotinamide–adenine dinucleotide-specific isocitrate dehydrogenase from pea mitochondria

1969 ◽  
Vol 113 (5) ◽  
pp. 813-820 ◽  
Author(s):  
G. F. Cox ◽  
D. D. Davies
Keyword(s):  
Density Gradient ◽  
Isocitrate Dehydrogenase ◽  
Nicotinamide Adenine Dinucleotide ◽  
Substrate Concentration ◽  
Density Gradient Centrifugation ◽  
Gradient Centrifugation ◽  
Nicotinamide Adenine ◽  
Ph Optimum ◽  
Effects Of Ph ◽  
Metabolic Significance

1. The effect of pH on the co-operative activation of the NAD-specific isocitrate dehydrogenase from pea mitochondria by isocitrate is shown. 2. The interlinked effects of pH on the affinity of the NAD-specific isocitrate dehydrogenase for isocitrate and the dependence of the pH optimum on the substrate concentration are presented. 3. A consideration of the conditions of pH and substrate concentration under which citrate activates the NAD-specific isocitrate dehydrogenase demonstrates similarities between the binding of isocitrate and citrate. 4. A comparison of the effects of citrate and pH on the gross structure of the enzyme is investigated by density-gradient centrifugation. 5. The kinetic interpretations of these results are briefly considered. 6. The metabolic significance of these studies is discussed.

scholarly journals PERMEABILITY OF MICROSOMAL MEMBRANES ISOLATED FROM RAT LIVER

1973 ◽  
Vol 56 (3) ◽  
pp. 762-776 ◽  
Author(s):  
Robert Nilsson ◽  
Elisabeth Peterson ◽  
Gustav Dallner
Keyword(s):  
Molecular Weight ◽  
Rat Liver ◽  
Nicotinamide Adenine Dinucleotide ◽  
Liver Microsomes ◽  
Nicotinamide Adenine Dinucleotide Phosphate ◽  
Nicotinamide Adenine ◽  
Rat Liver Microsomes ◽  
Osmotic Response ◽  
Microsomal Membranes ◽  
Reduced Nicotinamide Adenine Dinucleotide

Water compartments, permeability, and the possible active translocation of various substances in rat liver microsomes were studied by using radioactive compounds and ultracentrifugation. The total water of the microsomal pellet, 3.4 µl/mg dry weight, is the sum of water in the extramicrosomal and intramicrosomal spaces, or 56 and 44%, respectively. Sucrose space accounts for 77% of the intramicrosomal water and the hydration water ∼ 14%, leaving almost no sucrose-impermeable space when using the ultracentrifugation approach. With increasing sucrose concentration, microsomes do not show an osmotic response. The intramicrosomal water decreases greatly in the presence of Cs+ and Mg++ in rough but not in smooth microsomes. Uncharged substances of molecular weight of up to at least 600 freely penetrate microsomal membranes, which already become impermeable to charged substances at a molecular weight of 90. These substances also induce an osmotic response. The vesicles can be made permeable to charged substances after water treatment and cooling, which, however, does not increase glucose-6-phosphatase and inosine diphosphatase (IDPase) activities, and these enzymes can still be activated by deoxycholate. IDPase, reduced nicotinamide adenine dinucleotide-cytochrome c reductase, and reduced nicotinamide adenine dinucleotide phosphate-dependent hydroxylation reactions, performed in vitro, also disproved the hypothesis of an accumulation of charged substances inside of vesicles of being a major pathway. The products of the enzymic reactions as well as the glucuronidated form of a hydroxylated product can be recovered on the cytoplasmic side of membranes, and little accumulation occurs in the intravesicular compartment.

Sign in / Sign up

Export Citation Format

Share Document