Tyrosine-67 in cytochrome c is a possible apoptotic trigger controlled by hydrogen bonds via a conformational transition.

We found that cyt c Y67H and Y67R variants represent a state which resembles the conformational intermediate state in cyt c with high peroxidase activity; and also the hydrogen bond network around Tyr67 is associated with the conformational transition of cyt c; these suggest that the hydrogen bond network around Tyr67 is essential in maintaining the cyt c functioning not only as an electron transfer protein but also probably as a trigger in apoptosis.