The carbon monoxide-binding hemoprotein reducible by hydrogen peroxide in microsomal fractions of pea seeds

There exist at least two kinds of CO-binding hemoproteins in microsomal fractions of germinating pea (Pisum sativum) seeds. One of them is cytochrome P-450 and the other is also a protoheme protein (judged from its pyridine hemochrome spectrum), which is not hitherto reported. The content of the new hemoprotein is much higher than that of cytochrome P-450 in the early stage of germination. During germination the former decreases and the latter increases. The new hemoprotein is not appreciably reduced by sodium dithionite alone within a few minutes, but, it is easily reduced by dithionite in the presence of methyl viologen and also by hydrogen peroxide when CO is present. The addition of hydrogen peroxide to pea microsomes in the absence of CO causes destruction of the hemoprotein and also decolorization of endogenous carotenoid. Destruction of these components is brought about by organic hydroperoxides independently of the presence of CO. In the presence of hydroxylamine, the addition of hydroperoxides to the microsomes results in the formation of an absorption spectrum similar to the spectra of ferrous-NO complexes of protoheme proteins. When N,N-dimethyl p-phenylenediamine is present, the reaction of pea microsomes with hydroperoxides gives a spectrum similar to that of the ferryl form of myoglobin. The reactions of the hemoprotein with hydroperoxides are inhibited by alpha,alpha'-dipyridyl and aniline, with which pea microsomes form binding spectra. The microsomes form a rather stable difference spectrum with hydroxylamine. However, the hemoprotein is destroyed when hydroxylamine is added to the microsomes in the reduced state.