THE ADP ATP CARRIER IS THE 32-KILODALTON RECEPTOR FOR AN NH2-TERMINALLY MYRISTYLATED SRC PEPTIDE BUT NOT FOR PP60(SRC) POLYPEPTIDE

Membrane binding of pp60src is initiated via its myristylated NH2 term inus. To identify a candidate pp60src docking protein or receptor in t he membrane, a radiolabelled peptide corresponding to the pp60src NH2- terminal membrane binding domain was cross-linked to fibroblast membra nes and found to specifically label a 32-kDa protein. This protein was purified by appending an affinity tag to the peptide probe so that th e cross-linked complex could be isolated via affinity chromatography. Microsequencing indicated that the 32-kDa protein was the mitochondria l ADP/ATP carrier (AAC). This result was further confirmed by the abil ity of an antibody to the AAC to immunoprecipitate the cross-linked co mplex, by the ability of certain inhibitors of the AAC to block cross- linking, and by membrane fractionation to show that complex formation occurred essentially exclusively in the mitochondrial fraction. While the AAC bound the myristyl-src peptide in a specific manner both in vi tro and in vivo, its localization to the inner membrane of the mitocho ndrion precludes its being a pp60src binding protein. An analysis of p p60v-src binding in vitro was consistent with this expectation. Thus, use of a myristyl-src peptide revealed an unexpected and previously un identified binding capacity of the AAC, most likely related to the abi lity of long-chain fatty acyl coenzyme As to serve as AAC inhibitors. The amphipathic nature of the pp60src NH2 terminus suggests alternativ e strategies for uncovering pp60src membrane binding species.