A hydrophobic quencher of protein fluorescence: 2,2,2-trichloroethanol

Previously the neutral fluorescence quenching probe, acrylamide, was employed to determine the degree of exposure of tryptophan residues in proteins. A less polar neutral quencher 2,2,2-trichloroethanol (trichloroethanol) was used in the present work to investigate whether it would preferentially interact with apolar regions of proteins. For most proteins studied, the degree of quenching by trichloroethanol is found to be about the same as with acrylamide. However, for human and bovine serum albumin hydrophobic interactions between trichloroethanol and these proteins occur, leading to an exalted quenching. The fluorescence quencher thus senses the presence of a hydrophobic domain in the vicinity of the tryptophan residues in these proteins. Trichloroethanol is shown to induce conformational changes in certain proteins and to be a potentially useful quencher for proteins having predominantly tyrosine emission.