F-19 NUCLEAR-MAGNETIC-RESONANCE INVESTIGATION OF STEREOSELECTIVE BINDING OF ISOFLURANE TO BOVINE SERUM-ALBUMIN

Whether proteins or lipids are the primary target sites for general an esthetic action has engendered considerable debate. Recent in vivo stu dies have shown that the S(+) and R(-) enantiomers of isoflurane are n ot equipotent, implying involvement of proteins. Bovine serum albumin (BSA), a soluble protein devoid of lipid, contains specific binding si tes for isoflurane and other anesthetics. We therefore conducted F-19 nuclear magnetic resonance measurements to determine whether binding o f isoflurane to BSA was stereoselective. Isoflurane chemical shifts we re measured as a function of BSA concentration to determine the chemic al shift differences between the free and bound isoflurane. K-D was de termined by measuring the F-19 transverse relaxation times (T-2) as a function of isoflurane concentration. The binding duration was determi ned by assessing increases in 1/T-2 as a result of isoflurane exchangi ng between the free and bound states. The S(+) and R(-) enantiomers ex hibited no stereoselectivity in chemical shifts and K-D values (K-D = 1.3 +/- 0.2 mM, mean +/-SE, for S(+), R(-), and the racemic mixture). Nonetheless, stereoselectivity was observed in dynamic binding paramet ers; the S(+) enantiomer bound with slower association and dissociatio n rates than the R(-).