Properties of nitrite reductase from Cucurbita pepo

Nitrite reductase purified to homogeneity from vegetable marrow contains 2 atoms Fe/mol. Enzyme-bound iron exchanged extremely slowly with ⁵⁹-Fe in solution. Acid-acetone extracts of the enzyme have a spectrum which is consistent with the presence of a sirohaem prosthetic group. Inhibition by mersalyl, which partially bleaches the enzyme, is reversible by glutathione only if this is added within a few min of mersalyl. The absorption spectra of the reduced and autoxidised enzyme and of the nitrite, cyanide and CO complexes are described. Amino acid composition data are given. The hydroxylamine reductase activity of the purified enzyme was 0.2% of nitrite reductase activity.