Identification of an essential β chain lysine residue from bovine heart mitochondrial ATPase specifically modified with nitrobenzofurazan

A tetrapetide containing an essential lysine residue chemically modified with the nitrobenzofurazan group has been purified from bovine heart mitochondrial ATPase. The composition of the peptide indicates that this lysine is residue 401 in the sequence of a beta chain. The modification was achieved by incubation at pH 9 of ATPase that had been previously labelled on a single essential tyrosine residue by reaction of the enzyme with 4-chloro-7-nitrobenzofurazan. The specific transfer of the nitrobenzofurazan group from the tyrosine residue to a particular lysine residue is consistent with the previously demonstrated intramolecular character of this transfer reaction.