MINIMUM STRUCTURAL REQUIREMENT FOR AN INHALATIONAL ANESTHETIC BINDING-SITE ON A PROTEIN TARGET

The present study makes use of direct photoaffinity labeling and fluor escence and circular dichroism spectroscopy to examine the interaction of the inhalational anesthetic halothane with the uncharged alpha-hel ical form of poly(L-lysine) over a range of chain lengths. Halothane b ound specifically to long chain homopolymers (190 to 1060 residues), r eaching a stable stoichiometry of 1 halothane to 160 lysine residues i n polymers longer than 300 residues. Halothane bound only non-specific ally to an alpha-helical 30 residue polymer and to all of the polymers in their charged, random coil form. The data suggest that halothane b inding is a function of supersecondary structure whereby intramolecula r helix-helix clusters form in the longer polymers, resulting in the c reation of confined hydrophobic domains. Circular dichroism spectrosco py cannot demonstrate changes in poly(L-lysine) secondary structure at any chain length with up to 12 mM halothane, suggesting that extensiv e hydrogen bond disruption by the anesthetic does not occur.