Study of Heme‐protein Linkage in Cytochrome b₂

An investigation of heme ligands in cytochrome b 2 has been attemptd by means of rose bengal sensitized photooxidation of “apo” and “holo” cytochrome b 2 core. When “apo” cytochrome b 2 core is photooxidizxed heme binding sites are progressively lost and histidine residues selectively destroyed. In “holo” cytochrome b 2 core the presence of the heme prosthetic group prevents the photooxidation of histidines. It is concluded tat at least one histidine, or possibly two, is involved as an iron ligand. Evidence is given that cysteine residues are not implicated in the heme binding. A methionine‐iron bond does not seem to exist.