Binding of the active metabolite of chloral hydrate, 2,2,2-trichloroethanol, to serum albumin demonstrated using tryptophan fluorescence quenching.

Chloral hydrate, a sedative/hypnotic agent widely used in the pediatric population, is converted to the active metabolite 2,2,2-trichloroethanol (TCE) in the liver. Tryptophan fluorescence quenching has been used previously to show that halothane and chloroform bind saturably to serum albumin, and a similar approach is used here to demonstrate that TCE also binds to albumin. TCE quenches the steady-state tryptophan fluorescence of bovine serum albumin (BSA) in a concentration-dependent, saturable manner with a K(D) = 3.3 +/- 0.3 mmol/l. Unlike halothane and chloroform, however, TCE also elicits a concentration-dependent blue-shift in the fluorescence emission spectrum of BSA and human serum albumin. This indicates that TCE induces a conformational change in the protein, causing the tryptophan to experience a change in its chemical environment, thus shifting the peak of the emission spectrum. Circular dichroism spectroscopy revealed a decrease in the alpha-helical content of BSA from 65.8 +/- 0.4 to 62.9 +/- 0.6% when TCE was present at a concentration of 30 mmol/l, providing further evidence for a conformational change. There is evidence that TCE potentiates the action of ligand-gated ion channels such as the GABA(A) and 5-HT(3) receptors, and the present results suggest that anesthetic alcohols may act by binding to these proteins and inducing structural changes that may in turn alter protein function. Copyright 2002 S. Karger AG, Basel