Occurrence of nitrite reductase in citrus leaves

Evidence is presented for the presence of nitrite reductasein citrus leaves. The enzyme has a Km for nitrite of 45 mu andis inhibited by cyanide. However, unlike citrus nitrate reductase(l), it is probably not a metalloflavo protein, although itmay be related to iron. In addition to the enzymatic nitrite reduction, non-enzymaticnitrite reduction was present in citrus leaf preparations. Underin vivo assay conditions nitrite reduction in one-month-oldleaves was not inhibited by cyanide, in contrast with three-month-oldleaves in which nitrite reduction was almost completely inhibited.Thus it appears that in very young citrus leaves most of thenitrite reduction is non-enzymatic. ¹ Contribution from The Volcani Center, Agricultural ResearchOrganization, P. O. B. 6, Bet Dagan, Israel. Series 1972.........2256AE. (Received November 28, 1972; )