Enzyme-activity Control

Availability of the substrate, NADH and nitrate would be an important determinant of the rate of nitrate assimilation. In addition, there are number of substances which are known to cause reversible inactivation of nitrate reductase under reducing condition (figure)

Figure: regulation of assimilatory nitrate reductase (NR), reversible inactivation of NR by combination with hydroxylamine, cyanide, or superoxide and reversal of this inactivation by blue light in the presence of flavin; inactivation by combination with specific binding proteins or by limited proteoiysis. Enzyme synthesis is regulated by positive effector-nitrate, plastidic factor, light and negative effectors derived from ammonia.