Subunits of Bakers' Yeast Cytochrome b2 ( l ‐Lactate Cytochrome c Oxidoreductase)

1.1 to 1.4 residues of lysine were found as N‐terminal amino acid in crystallized cytochrome b2, 1 residue of alanine and variable amounts of lysine as C‐terminal amino acids. Examination of the end groups of the purified S‐carboxymethylated subunits showed that, besides lysine at the N‐terminus in both chains, alanine at the C‐terminal of the light chain and lysine at the C‐terminal of the heavy chain, other end groups were detected in minor amounts. Digestion of the native protein with carboxypeptidase B led to the finding that a protease still contaminates preparations of type II cytochrome b2. Phenylmethylsulfonyl fluoride is an inhibitor of this protease, the action of which can explain the observed microheterogeneity.