Oxidative deformylation of 4-hydroxy[14C]methylene-5alpha-cholest-7-en-3-one and oxidative demethylation of [30,31-14C]4,4-dimethyl-5alpha-cholest-7-en-3beta-ol by rat liver microsomes have been compared with regard to the manner in which electrons are introduced from both NADH and NADPH. Evidence suggests that NADH and NADPH support oxidation of both substrates via separate routes of electron ...

In vitro formation of reduced nicotinamide adenine dinucleotide phosphate (NADPH)-nitrate reductase (NADPH: nitrate oxido-reductase, EC 1.6.6.2) has been attained by using extracts of the nitrate reductase mutant of Neurospora crassa, nit-1, and extracts of either photosynthetically or heterotrophically grown Rhodospirillum rubrum, which contribute the constitutive component. The in vitro forma...

The NADPH-dependent 2,5-diketo-D-gluconic acid (2,5-DKG) reductase enzyme is a required component in some novel biosynthetic vitamin C production processes. This enzyme catalyzes the conversion of 2,5-DKG to 2-keto-L-gulonic acid, which is an immediate precursor to L-ascorbic acid. Forty unique site-directed mutations were made at five residues in the cofactor-binding pocket of 2,5-DKG reductas...

The mammalian plasma membrane (PM) NADH-oxidoreductase (PMOR) system is a multi-enzyme complex located in the plasma membrane of all eukaryotic cells, harboring at least two distinct activities, the plasma membrane NADH-ferricyanide reductase and the NADH-oxidase. To assess the behaviour of the two activities of the PMOR system, we measured the NADH-ferricyanide reductase and NADH-oxidase activ...

Nitrate reductase activity in excised embryos of Agrostemma githago increases in response to both NO(3) (-) and cytokinins. We asked the question whether cytokinins affected nitrate reductase activity directly or through NO(3) (-), either by amplifying the effect of low endogenous NO(3) (-) levels, or by making NO(3) (-) available for induction from a metabolically inactive compartment. Nitrate...

The enzyme systems which catalyze the reduction of nitrate to nitrite have generally been classified into two broad types: (a) assimilatory nitrate reductase, which is responsible for the first step in the reduction of nitrate for the ultimate biosynthesis of nitrogen-containing cell constituents (e.g., amino acids aind purines and pyrimidines), and (b) respiratory or dissimilatory nitrate redu...

The standard procedure for the in ritro extraction of nitrate reductase from the tip region (0-2 cm) of the primary root of the maize (Zea mays L.) seedling indicated an activity of the enzyme approximately 5-fold higher than that obtained with an in vivo assay. In more mature regions of the primary root the ratio of in vitro to in vivo activity was much lower and in older seedlings was less th...

Rat adrenal mitochondria have an active rotenone-insensitive outer mitochondrial membrane NADH-semidehydroascorbate (NADH-SDA) reductase which supports cholesterol side chain cleavage at a rate equal to that supported by malate. Side chain cleavage activity supported by both of these electron donor systems is equally inhibited by cycloheximide. Catalase or butylated hydroxyanisole are required ...

A dihydroxyacetone phosphate (DHAP) reductase has been isolated in 50% yield from Dunaliella tertiolecta by rapid chromatography on diethylaminoethyl cellulose. The activity was located in the chloroplasts. The enzyme was cold labile, but if stored with 2 molar glycerol, most of the activity was restored at 30 degrees C after 20 minutes. The spinach (Spinacia oleracea L.) reductase isoforms wer...

In Oscillatoria chalybea, as in other cyanobacteria, nitrate reduction depends directly on photosynthetic activity. Hence, nitrate reduction occurs only in the light and appears inhibited when photosynthesis is inhibited by the herbicide DCM U. Growth o f Oscillatoria cells is pos­ sible on a variety o f exogenous nitrogen sources in the medium and appears largely independ­ ent on the type of n...