The interaction of rivanol with bovine serum albumin

Interaction of the cationic form of rivanol (6, 9-diamino-2-ethoxyacridine lactate) with native and modified bovine serum albumins (BSA) was studied by various physicochemical methods. Influence of pH and ionic strength on precipitation of BSA by rivanol was investigated. The amount of precipitate formed increased with pH above 7.0, and increasing the ionic strength reduced precipitation at any pH. Modification of basic groups of BSA resulted in increased precipitation below pH 8.0. Extensive methylation of COOH groups of BSA resulted in diminished or no precipitation. Presence of a soluble BSA-rivanol complex at pH 8.0 or above in the supernatant fluid was shown by electrophoresis. A number of physicochemical measurements failed to reveal significant changes in the BSA recovered from the BSA-rivanol complex. By means of equilibrium dialysis experiments, a plot of the binding data gave a straight line indicating the stoichiometric nature of the BSA-rivanol interaction. From these data the maximal number of binding sites ( n) was found to be 17 and the binding constant ( k) equal to 150. However, it was found that precipitation occurs upon the addition of more than 7 moles rivanol/mole albumin at pH 8.0, 0.10 μ. The general nature of the rivanol-BSA interaction resembles that of bivalent cations to carboxyl groups.