Binding of 2-(4'-hydroxyphenylazo)benzoic acid to bovine serum albumin characterized by optical spectroscopy and equilibrium dialysis.

Abstract

Binding of 2-(4'-hydroxyphenylazo)benzoic acid (HABA) to bovine serum albumin (BSA) was studied by equilibrium dialysis, by the spectrophotometric method and by the absorption spectra of bound HABA. Comparison of equilibrium dialysis with the spectrophotometric method clarified the presence of a undisclosed class of binding sites, which do not cause the spectral change at about 480 nm to HABA, on BSA. Two bands observed on the absorption spectra of bound HABA were attributed to differently perturbed two HABA molecules by BSA, the azo and hydrazone forms, and these two forms correspond to HABA molecules bound to non-metachromasy sites and metachromasy sites, respectively. The concentration of each from was calculated by using estimated molar extinction coefficient.