STUDIES ON CYTOCHROME C

II. FURTHER STUDY ON PROTEINASE DIGESTION OF BAKER'S YEAST CYTOCHROME C

Abstract

1. Yeast cytochrome c was modified by TCA-treatment and by boiling. These modified forms of cytochrome c are more susceptible to digestion by trypsin than the native form, in the following order: Oxidized, boiled yeast cytochrome c>Oxidized, TCA-treated yeast cytochrome c>Oxidized, native yeast cytochrome c>Reduced, native yeast cytochrome c>Oxidized, native bovine cytochrome c.
2. Native yeast cytochrome c in its reduced form is scarcely digested by bacterial proteinase and trypsin, while in its oxidized form is rapidly digested. The cytochrome c in its reduced form is digested after being oxidized by the catalytic action of the digested cytochrome c under aerobic, but not appreciably under anaerobic conditions.
3. Yeast cytochrome c modified by TCA-treatment or boiling shows almost the same absorption spectra as that of the native form, but when digested by bacterial proteinase and trypsin it shows spectra especially of the γ- and δ-bands which are different from those of the native form.
4. Modified yeast cytochrome c is reduced by yeast lactic dehydrogenase in the presence of lactate at almost the same initial rate as the native form, but the digested form is not reduced even under anaerobic conditions.
From these facts, the relation between the electron transfer by yeast cytochrome c and the configuration of its protein-moiety is discussed.
We would like to express our thanks to Messrs. T. Higashi, T. Yamanaka, and J. Yamashita for their help and discussion during this investigation, and to Mr. K. Fujii (Oriental Yeast Co., Ltd., Suita, Osaka, Japan) for his advices and for his supplying us with baker's yeast.