Studies on Cytochrome Oxidase

Hematin a isolated from purified cytochrome oxidase reacts with poly-r&sine and with proteins of high lysine content, such as histone, albumin, and globin, in neutral and alkaline media. At pH 11.6, spectral characteristics of these synthetic complexes are strikingly similar to those of cytochrome oxidase. Although absorbance indices differ, the positions of the band maxima are virtually the same in the oxidized, the reduced, the carbon monoxide-reduced, the borohydridetreated, and the borohydride-treated followed by carbon monoxide reduction forms. After borohydride reaction, the heme a in these complexes as well as in cytochrome oxidase is no longer extractable by acid-acetone. On the other hand, these characteristics are not shared when hematin (I is replaced by protohematin. Hematin a does not react with histidine, lysine, glutamic acid, aspartic acid, proline, alanine, polyglutamic acid, polyproline, or protamine in either neutral or alkaline media, or with polytyrosine in alkaline solutions under conditions similar to those used for polylysine, i.e. at less than 2 mg of nitrogenous compound per ml. However, the spectra of heme a in the presence of 5% lysine (but not other free amino acids tested, including methionine, histidine, and tyrosine) closely resemble those of the heme a-polylysine complex. Although hematin o reacts with polysarcosine and polyhistidine, the reaction differs from that with polylysine. From the data presented here, together with the behavior of cytochrome oxidase described previously (30), it is tentatively concluded that at least 1 lysine residue of cytochrome oxidase coordinates with the heme iron at pH 11.6, and another lysine residue forms a Schiff base with the formyl group on the porphyrin nucleus. The justification for the conclusion, along with certain reservations, has been pointed out.