Local anesthetic tetracaine influences the physical properties of globularproteins

The interaction of local anesthetic tetracaine (TTC) with globular protein- bovine serum albumin (BSA) was studied by the measurement of sound velocity and density. We showed, that in its native form, at pH 7, the TTC in a con centration of 0.1 mmol l(-1) resulted in an increase of adiabatic compressi bility of BSA, while practically no changes of adiabatic compressibility wa s observed, when native form has been lost or changed (at pH 3). The bindin g of TTC on BSA was shown by measurement fluorescence quenching. Addition o f TTC resulted BSA tryptophan fluorescence quenching that saturates at TTC concentration 1-3 mmol l(-1). The dissociation constant, K-d = 1.18 +/- 0.5 4 mmol l(-1), related to the binding of TTC to BSA was determined from fluo rescence quenching experiments. We assume that TTC incorporates into hydrop hobic core of BSA. This incorporation caused increase of BSA specific volum e and consequently the conformational freedom of polypeptid chain could be the main reason of increase of BSA adiabatic compressibility. (C) 2000 Else vier Science B.V. All rights reserved.