STUDIES ON CYTOCHROME A*

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Abstract
Cytochrome oxidase activity of purified cytochrome a is strongly inhibited by hydrazine, phenylhydrazine, hydroxylamine or Na bisulfite at 10- M. Dialysis can reactivate cytochrome a. The inhibition by the 5051[1961] BIOCHEMISTRY 51326-51337 hydrazine compounds is competitive, while that by hydroxyiamine and sulfite is noncompetitive. Among those inhibitors only hydroxyiamine is bound to haem Fe atom as evidenced by shifting of the adsorption bands to shorter wavelength, which is also the case with the reaction of hydroxyiamine with isolated hemin a or porphyrin a. The presence of formyl group in the haem moiety and the formation of oxime or hydrazone upon adding the aldehyde reagents are suggested.

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