Ichiro Sekuzu

Studies on cytochrome a VII. Physico-chemical properties of purified cytochrome a

This paper gives results of an investigation on the homogeneity and molecular state of preparations of cytochrome a solubilized with surface-active agents and studied by sedimentation experiments and electrophoresis. The sedimentation pattern of cytochrome a in the presence of the non-ionic detergent. Emasol 1130, shows a single homogeneous and symmetric monodispersed component, whereas in the presence of the ionic detergent, sodium cholate, the protein behaves as a polydispersed, aggregated system. Based upon experimental results indicating a sedimentation coefficient of 21.9 S, a diffusion constant of 3.58·10−7 cm2/sec and a partial specific volume of 0.72 ml/g, it si calculated that cytochrome a solubilized with Emasol 1130 has a molecular weight of approx. 530 000, whereas its minimum molecular weight calculated from its iron content is 100 000. Thus the existence of the rigid structure of a pentamer is indicated. It was, furthermore, found that by treatment with reagents such as sodium docecyl sulfate or urea the protein is split into smaller subunits. Based on these results, the molecular state of cytochrome a is discussed.

Studies on cytochrome a: IV. Reaction of cytochrome a with cytochromes c and c1

Abstract In the present paper, the important role played by cytochrome c in the cytochrome oxidase system is demonstrated by using highly purified praparatinos of cytochromes a , c 1 , and c 1 . Despite the fact that cytochrome a can be rapidly reduced by p -phenylene-diamine, the component is not oxidized by oxyge if cytochrome c is not present. The K m calculated for cytochrome c is similar to that found in particulate preparations. The addition of cytochrome c 1 has not effect on the cytochrome oxidase reaction. The reaction between cytochromes c 1 and a is very slow and is mediated by cytochrome c . On the basis of the above results, it is proposed that cytochrome c acts not only as an electron carrier between cytochromes c 1 and a but also as an essential constituent to form an active complex with cytochrome a in the cytochrome oxidase system. The reaction mechanism of teh cytochrome oxidase system is discussed on the basis of the above results.