Volume 272, Number 29,
Issue of July 18, 1997
pp. 17961-17965
©1997 by The American Society for Biochemistry and Molecular Biology, Inc.
Binding of the Volatile Anesthetic Chloroform to Albumin
Demonstrated Using Tryptophan Fluorescence Quenching
(Received for publication, February 12, 1997, and in revised form, April 2, 1997)
Jonas S.
Johansson
From the Department of Anesthesia and the Johnson Research
Foundation, University of Pennsylvania,
Philadelphia, Pennsylvania 19104
The site(s) of action of the volatile general
anesthetics remain(s) controversial, but evidence in favor of specific
protein targets is accumulating. The techniques to measure directly
volatile anesthetic binding to proteins are still under development.
Further experience with the intrinsic protein fluorescence quenching
approach to monitor anesthetic-protein complexation is reported using
chloroform. Chloroform quenches the steady-state tryptophan
fluorescence of bovine serum albumin (BSA) in a
concentration-dependent, saturable manner with a
Kd = 2.7 ± 0.2 mM. Tryptophan
fluorescence lifetime analysis reveals that the majority of the
quenching is due to a static mechanism, indicative of anesthetic
binding. The ability of chloroform to quench BSA tryptophan
fluorescence was decreased markedly in the presence of 50%
2,2,2-trifluoroethanol, which causes loss of tertiary structural
contacts in BSA, indicating that protein conformation is crucial for
anesthetic binding. Circular dichroism spectroscopy revealed no
measurable effect of chloroform on the secondary structure of BSA. The
results suggest that chloroform binds to subdomains IB and IIA in BSA,
each of which contains a single tryptophan. Earlier work has shown that
these sites are also occupied by halothane. The present study therefore
provides experimental support for the theory that structurally distinct general anesthetics may occupy the same domains on protein targets.