Nitrate reductase and related enzymes in Escherichia coli

Abstract

A system which reduces nitrate to nitrite, with di- or tri-phosphopyridine nucleotide as electron donor and vitamin K3 as electron carrier, has been found in E. coli. The transfer of electrons from pyridine nucleo-tides to vitamin K3 is catalysed by the constitutive menadione reductase. Nitrate reductase proper is an inducible enzyme which is associated with particulate matter. Nitrate reductase apparently involves some metal but not flavin. The effects of substrate concentration, pH and other factors have been investigated. Anaerobically, in addition to this pathway, nitrate reduction can take place through a system, apparently flavin-dependent, presumably related to the reduced diphosphopyridine nucleotide oxidase. The possible physiological significance of these two systems able to reduce nitrate is discussed.