Interaction between cytochrome C and di- and tripeptides.

By observing changes in the absorbance spectrum between 340 and 650 nm, we found that tyrosyltyrosylphenylalanine (TTP) interacts with cytochrome C (CC). TTP caused the characteristic changes of CC reduction, namely, an increased optical density at 524 and 550 nm and a hyperchromic shift at 416 nm. The apparent dissociation constant (Kd) was 2.9 x 10(-3) M. Most of the reducible CC at 20 uM concentration was reduced by 10 mM TTP. TTP was more potent than all other peptides tested, including the previously reported tyrosylphenylalanine. That the carboxyl terminal phenyl group was essential for reduction was shown by comparing variously substituted di- and tripeptides. Reduction by TTP increased with increasing pH and buffer concentration at constant pH. A combination of superoxide dismutase and catalase failed to inhibit the reduction. We found no effect of TTP on O2 consumption of isolated intact mitochondria. Our data demonstrate that small peptides can serve as probes of the topography and electron density of CC and that the TTP-CC interaction may provide insight as an analog of in-vivo processes.