Assimilatory nitrate reductase from Chlorella. Effect of ionic strength and pH on catalytic activity

Initial velocity studies of Chlorella nitrate reductase showed that increased ionic strength stimulated NADH:nitrate reductase activity by increasing both Vmax and Km for nitrate. Examination of the effect of ionic strength on the various partial activities of nitrate reductase revealed that while N...

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Bibliographic Details
Published in:The Journal of biological chemistry 1986-10, Vol.261 (30), p.14125-14129
Main Authors: Kay, C J, Barber, M J
Format: Article
Language:English
Subjects:
ACTIVIDAD CATALITICA
ACTIVITE CATALYTIQUE
Analytical, structural and metabolic biochemistry
ASIMILACION
ASSIMILATION
Biological and medical sciences
CATALYTIC ACTIVITY
Chlorella - enzymology
CHLORELLA VULGARIS
CHLOROPHYCEAE
Enzymes and enzyme inhibitors
Fundamental and applied biological sciences. Psychology
Hydrogen-Ion Concentration
Kinetics
NAD - metabolism
Nitrate Reductase
Nitrate Reductases - metabolism
Osmolar Concentration
OXIDOREDUCTASES
OXIDORREDUCTASAS
OXYDOREDUCTASE
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Summary:Initial velocity studies of Chlorella nitrate reductase showed that increased ionic strength stimulated NADH:nitrate reductase activity by increasing both Vmax and Km for nitrate. Examination of the effect of ionic strength on the various partial activities of nitrate reductase revealed that while NADH:ferricyanide and reduced methyl viologen:nitrate reductase activities were unaffected by ionic strength, NADH:cytochrome c and reduced flavin:nitrate reductase activities were inhibited and stimulated by increased ionic strength, respectively. Comparison of the rates for the partial activities indicated electron transfer from heme to molybdenum to be the rate-limiting step in enzyme turnover. The pH optimum for NADH:nitrate reductase activity was found to be 7.9 while values for the partial activities ranged from 5.5 to 8.1. Phosphate was found to stimulate both NADH:nitrate and reduced methyl viologen:nitrate reductase activities indicating the molybdenum center as the site of interaction.
ISSN:0021-9258
1083-351X
DOI:10.1016/S0021-9258(18)66991-1