S-Cys CH3 CH=CH2 CH3 CHCH Cys-S CH2=CH CH3 CH3CH Te- CH3 CH2CH2COO CH3 CH2CH2COO CH3 CH2CH2COO- CH3 CH2CH2COO Iron protoporphyrin IX Heme C (in b-type cytochromes) (in c-type cytochromes) CH3 CH=CH2 OH CH3 CH2-CH CH. CH3 CH3 CH2CH2COO CHO CH2CH2COO Heme A (in a-type cytochromes) 网