Catalytic and noncatalytic nucleotide binding sites of the Escherichia coli F1 ATPase Amino acid sequences of β‐subunit tryptic peptides labeled with 2‐azido‐ATP

Abstract

Under appropriate conditions tight, noncovalent binding of 2-azido-adenine nucleotides to either catalytic or noncatalytic binding sites on the E. coli F₁-ATPase occurs. After removal of unbound ligands, UV-irradiation results primarily in the covalent incorporation of nucleotide moieties into the β-subunit in both catalytic and noncatalytic site labeling experiments. Minor labeling of the α-subunit was also observed. After trypsin digestion and purification of the labeled peptides, microsequencing studies identified two adjacent β-subunit tryptic peptides labeled by 2-azido-ADP or -ATP. These β-subunit peptides were labeled on tyrosine-331 (catalytic sites) and tyrosine-354 (noncatalytic sites) in homology with the labeling patterns of the mitochondrial and chloroplast enzymes.