Local anesthetic tetracaine influences the physical properties of globular proteins

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 concentration of 0.1 mmol l–1 resulted in an increase of adiabatic compressibility of BSA, while practically no changes of adiabatic compressibility was observed, when native form has been lost or changed (at pH 3). The binding of TTC on BSA was shown by measurement fluorescence quenching. Addition of TTC resulted BSA tryptophan fluorescence quenching that saturates at TTC concentration 1–3 mmol l–1. The dissociation constant, Kd=1.18±0.54 mmol l–1, related to the binding of TTC to BSA was determined from fluorescence quenching experiments. We assume that TTC incorporates into hydrophobic core of BSA. This incorporation caused increase of BSA specific volume and consequently the conformational freedom of polypeptid chain could be the main reason of increase of BSA adiabatic compressibility.