Tyrosine-311 of a beta chain is the essential residue specifically modified by 4-chloro-7-nitrobenzofurazan in bovine heart mitochondrial ATPase

A peptide containing an essential tyrosine residue, modified with the nitrobenzofurazan group, has been purified from bovine heart mitochondrial ATPase. The composition of the peptide indicates that this tyrosine is residue 311 in the sequence of a beta chain. The problem of the instability of the tyrosyl-nitrobenzofurazan bond was overcome by working throughout at relatively acidic pH and using pepsin digestion of the enzyme.