Nitrate reductase NADPH specific

In addition to the substrate, nitrate, regulating the production of nitrate reductase, it has been reported that in some instances the product nitrite can stimulate the appearance of nitrate reductase (Ingle et al., 1966 Kaplan cr al., 1978). The aromatic nitro compound, chloramphenicol, and other organic nitro compounds have been shown to regulate the level of nitrate reductase in rice seedling (Shen, 1972a,b). Not only is the level of nitrate reductase influenced by these compounds but the nucleotide specificity is changed in favor of NADPH. 

Nitrate reductase, the first enzyme in the nitrate assimilation pathway, catalyzes the reduction of nitrate to nitrite. This requires two electrons which are donated by either NADH or NADPH in the eukaryotic NRs. The NADH-spe-cific NRs (EC 1.6.6.1) are found in most higher plants and numerous eukaryotic algae while the NADPH-specific NRs (EC 1.6.6.3) are found in the fungi. The NAD(P)H-bispecific NRs (EC 1.6.6.2) occur in some higher plant and algae species. The prokaryotic NRs which utilize a variety of electron donors, including ferredoxin, reduced pyridine nucleotides, and respiratory intermediates, will not be considered in this article (see Stewart, 1988). 

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