Inactivation of cytochrome cd1 by hydrazines

The dissimilatory nitrite reductase, cytochrome cd1, from Pseudomonas aeruginosa (ATCC 19429) was irreversibly inactivated by methyl- or phenylhydrazine but was only reduced by hydrazine itself. The reaction required oxygen and several turnovers, approximately four, of the cytochrome acting to transfer reducing equivalents from phenylhydrazine to oxygen. The reaction with methyl- or phenylhydrazine altered the visible spectrum of the cytochrome. Bands characteristic of reduced heme c appeared plus new features that were not characteristic of either oxidized or reduced heme d1. Extraction of the heme from phenylhydrazine-treated cytochrome yielded a covalently modified form of the original heme d1. Visible, 1H NMR, and mass spectra were obtained on the purified modified heme and on the metal-free esterified derivative. The spectroscopic data indicate that the modification was the regiospecific substitution of the 5 meso-proton by a phenyl group.