Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.7.1.2 (nitrate reductase)
 3,861 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A simple and rapid procedure to make yeast cells permeable by agitating with toluene-ethanol, (TE) 1:4, v/v was developed. The permeated cells retained their ability to catalyze certain enzyme reactions. Temperature and duration of agitation during TE treatment played an important role in retention of the catalytic potential of permeated cells. The in situ assay using permeated cell preparations was more sensitive even in the absence of added cofactors than in the vitro assay in detecting assimilatory nitrate reductase (NAD(P)H:nitrate oxidoreductase, EC 1.6.6.2) (NAR) activity in Candida utilis. Using in situ assay technique, different mechanisms regulating the biosynthesis of NAR in C. utilis were investigated. Nitrogen starvation did not lead to derepression of NAR. NO3-ions were absolutely essential for induction and maintenance of high levels of NAR activity. Cells grown on ammonium nitrate possessed relatively lower levels of NAR. Kinetics of NAR induction were followed as a function of time and inducer concentration. The influence of various cations on the induction of NAR by nitrate was investigated. A wide range of D-amino acids induced NAR synthesis. Of 22 L-amino acids tested only phenylalanine induced significant levels of NAR. Various intermediates of the pathway of nitrate reduction influenced the rate of NAR induction. There was a rapid disappearance of in vivo activity of the enzyme of induced yeast cells on nitrogen starvation, and the rate of loss was accelerated by the presence of NH4+.
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PMID:Regulatory properties of yeast nitrate reductase in situ. 94 16

A simple approach for rapid assay of enzymes in large numbers of samples of whole cells of yeast is described. The technique involves treatment of yeast cells with toluene dissolved in ethanol (1:4, v/v; TE), rendering them selectively permeable to small molecules, while letting the enzymes remain intracellular and catalytically active but accessible to exogenously added assay reagents. The permeated cell preparations permit rapid assay of nitrate reductase activity in situ [P. V. Choudary and G. Ramananda Rao (1976) Current Sci. 45, 324-327]. Investigation of enzyme kinetic parameters such as pH optima, temperature dependence, and substrate saturation, which involves several samples and needs to be investigated very rapidly and accurately, is greatly facilitated by permeated cells prepared from a very small culture of cells, eliminating the need for elaborate preparations of cell extracts. By using permeabilized cell preparations, the need to supplement the reaction mixture with expensive cofactors can also be obviated to a large extent. Further, the enzyme activity displays a broader range of tolerance in situ to variations in reaction conditions compared to that in vitro. Permeabilized cell preparations thus seem to present the enzymes in the form of relatively less disintegrated functional complexes, making them a valuable tool in biochemical and cell biological investigations, and facilitate the correlation of in vitro data with the in vivo phenomena more confidently.
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PMID:A simple micromethod for rapid kinetic analyses of yeast enzymes in situ. 654 57