A disulfide reductase in spores of Bacillus cereus T

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.

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

Biochemical Journal ◽

10.1042/bj1320215 ◽

1973 ◽

Vol 132 (2) ◽

pp. 215-221 ◽

Cited By ~ 15

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.

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PERMEABILITY OF MICROSOMAL MEMBRANES ISOLATED FROM RAT LIVER

The Journal of Cell Biology ◽

10.1083/jcb.56.3.762 ◽

1973 ◽

Vol 56 (3) ◽

pp. 762-776 ◽

Cited By ~ 87

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.

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