Amino acid resolution of halothane binding sites in serum albumin

Saturable binding of various inhaled anesthetics to serum albumin has been shown with a variety of approaches, In order to determine the location of halothane binding sites in serum albumin, both human and bovine serum albumins (HSA and BSA) were photolabeled with [C-14]halothane, and subjected to proteolysis and microsequencing, BSA was found to have a higher affinity for halothane than HSA, and it contained two specifically labeled sites, One site was characterized by diffuse labeling from Trp(212)-Leu(217), and the other by a more discrete and higher affinity labeling at Trp(134)-Gly(135). HSA contained only a single labeled site, and although lower affinity, was determined to be analogous to BSA Trp(212). The position 130-140 region of HSA, having a leucine instead of tryptophan at position 134, was not labeled, These results demonstrate specific and discrete binding of an inhaled anesthetic to a mammalian-soluble protein, and further suggest the importance of aromatic residues as one feature of inhaled anesthetic binding sites.