Exploration of nucleotide binding sites in the mitochondrial membrane by 2-azido-[α-32 P]ADP

Abstract
The ADP/ATP carrier of beef heart mitochondria is able to bind 2‐azido‐[α‐32P]ADP in the dark with a K d value of ∼ 8 μM. 2‐Azido ADP is not transported and it inhibits ADP transport and ADP binding. Photoirradiation of beef heart mitochondria with 2‐azido‐[α‐32P]ADP results mainly in photolabeling of the ADP/ATP carrier protein; photolabeling is prevented by carboxyatractyloside, a specific inhibitor of ADP/ATP transport. Upon photoirradiation of inside‐out submitochondrial particles with 2‐azido‐[α‐32P]ADP, both the ADP/ATP carrier and the β subunit of the membrane‐bound F1‐ATPase are covalently labeled. The binding specificity of 2‐azido‐[α‐32P]ADP for the β subunit of F1‐ATPase is ascertained by prevention of photolabeling of isolated F1 by preincubation with an excess of ADP.