Studies on the Electron Transfer System: LVII. THE NEAR INFRARED ABSORPTION BAND OF CYTOCHROME OXIDASE

Abstract

A broad spectral absorbance band in the near infrared region of cytochrome oxidase* (cf. Fig. 1) was first reported by Griffiths and Wharton (2). They observed that this band near 830 rnp disappeared on complete reduction of the enzyme by substrate and reappeared on reoxidation. The rate of these changes was roughly equivalent to the rate of the changes observed in the a-peak at 605 rnp. In addition, they found that in the presence of cyanide the chromophore could be reduced but could not be reosidized. Recent,ly, Gibson and Greenwood2 observed, through the use of rapid reaction techniques, that the kinetics of the changes in the absorbance of cytochrome oxidase in the near infrared region and in the or-band were essentially identical, These data support the hypothesis that the chromophore absorbing near 830 rnp is an integral component of cytochrome oxidase, but they do not identify the chromophore. The accumulat’ing evidence that many copper-containing prot,eins exhibit absorption bands in the near infrared region (3-6), together with the demonstration that purified preparations of cytochrome oxidase contain copper (2, 7-12), directed our attention toward the possibliity that this metal may be a constituent of the chromophore in question. In this communication, experiments are described that establish a precise correlation among the intensity of the near infrared band, the copper content, and specific activity. This correlation persists as the values of these entities are decreased or obliterated by a variety of treatments and are partially restored by others.