Nitrate Reductase and Soluble Cytochrome c Reductase(s) in Higher Plants

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Abstract
The 4S cytochrome c (Cyt c) reductase activity of several plant spp. was markedly stimulated by cyanide and ferrocyanide but those of the 8S nitrate reductase component and other particulate components of the maize (Zea mays L.) scutellum by comparison, were increased only slightly. The effect of cyanide and ferrocyanide was not due to elimination of cytochrome oxide interference but resulted from the stimulation of NADH-dependent reduction of Cyt c. A 4S Cyt c reductase component which was isolated by ammonium sulfate fractionation and diethylaminoethyl-cellulose chromatography was found to be stimulated markedly by cyanide and ferrocyanide. The remaining 4S Cyt c reductase, which was insensitive to cyanide and ferrocyanide, was also fractionated with ammonium sulfate into 2 components. One of these, like the 8S Cyt c reductase, was sensitive to a protease from the maize roots which is relatively specific for nitrate reductase. This 4S Cyt c reductase species could be a subunit of nitrate reductase.
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