Identification of amino acid residues photolabeled with 2-azido[.alpha.-32P]adenosine diphosphate in the .beta. subunit of beef heart mitochondrial F1-ATPase

Abstract

When beef heart mitochondrial F1-ATPase is photoirradiated in the presence of 2-azido[.alpha.-32P]adenosine diphosphate, the .beta. subunit of the enzyme is preferentially photolabeled [Dalbon, P., Boulay, F., and Vignais, P. V. (1985) FEBS Lett. 180, 212-218]. The site of photolabeling of the .beta. subunit has been explored. After cyanogen bromide cleavage of the photolabeled .beta. subunit, only the peptide fragment extending from Gln-293 to Met-358 was found to be labeled. This peptide was isolated and digested by trypsin or Staphylococcus aureus V8 protease. Digestion by trypsin yielded four peptides, one of which spanned residues Ala-338-Arg-356 and contained all the bound radioactivity. When trypsin was replaced by V8 protease, a single peptide spanning residues Leu-342-Met-358 was labeled. Edman degradation of the two labeled peptides showed that radioactivity was localized on the following four amino acids: Leu-342, Ile-344, Tyr-345, and Pro-346.