Photoaffinity labeling of mitochondrial proteins with 2-azido [32P]palmitoyl CoA

A long-chain fatty acyl CoA photolabel, 2-azido [32P]palmitoyl CoA, was synthesized and its covalent interaction with mitochondrial membrane proteins examined. On binding of 2-azido [32P]palmitoyl CoA to beef heart mitochondria, two polypeptides were primarily labeled, the 30 kDa ADP/ATP carrier and a 41 kDa protein of unknown identity. Carboxyatractyloside and palmitoyl CoA completely protected against labeling of the 30 kDa protein indicating that it was the ADP/ATP carrier. With inverted submitochondrial particles, only the 30 kDa polypeptide was labeled by 2-azido [32P]palmitoyl CoA. The labeling was inhibited by bongkrekic acid and palmitoyl CoA but not carboxyatractyloside, providing evidence that the ADP/ATP carrier was covalently bound from the matrix side of the membrane. In brown adipose tissue mitochondria, 2-azido [32P]palmitoyl CoA photolabeled the ADP/ATP carrier and the 32 kDa uncoupling protein with some minor labeling of 36 and 68 kDa polypeptides. The results indicated that this physiological photolabeling reagent with the azido group on the CoA portion of the molecule interacts like 2-azido ADP with nucleotide binding sites of a number of important enzymes in cell metabolism. Moreover, the evidence strongly supports the hypothesis that long chain fatty acyl CoA esters are natural ligands for key nucleotide binding proteins.