DEGRADATION OF YEAST CYTOCHROME-C DEPENDENT AND INDEPENDENT ON ITS PHYSIOLOGICAL PARTNERS

Altered iso-l-and iso-a-cytochromes c, with certain amino acid replace ments, occur at diminished levels due to degradation in the yeast Sacc haromyces cerevisiae. A subclass of the labile isocytochromes c are si gnificantly protected from degradation by the presence of cytochromes a as and cl, the physiological partners of cytochrome c. We have inves tigated the degradation that is dependent on physiological partners by examining the levels of iso-1-cytochrome c having all or most amino a cid replacements at positions 6, 41, 52, and 78, in both rho(+) strain s and rho(-) strains, which lacks cytochrome a.a(3). In addition, we h ave examined some of these replacements in strains also having the N52 I replacement, which suppresses a variety of abnormal iso-l-cytochrome s c, including those whose degradation is either dependent or independ ent on the physiological partners. Although some degree of preferentia l rho(-)-dependent reductions was observed for iso-1-cytochromes c hav ing replacements at each of the 6, 41, 52, and 78 sites, prominent eff ects of rho(+)/rho- ratios of approximately 100/0 to 30/0 were observe d for iso-1-cytochromes c having replacements mainly at the 41, 52, an d 78 sites, but not the G6 site. We suggest that prominent degradation dependent on physiological partners mag be restricted to certain regi ons of the cytochrome c molecule. Furthermore, we suggest that the reg ion of the largest confirmational difference between oxidized and redu ced cytochrome c appears to be particularly protected by interactions with its physiological partners. (C) 1998 Academic Press.