The interaction of bovine plasma albumin with cationic detergents at pH9

The interaction of bovine plasma albumin (BPA) with tetradecyltri-methylammonium bromide (TTAB) was studied at pH 9.0. When the system BPA-TTAB was analyzed by the gel electrophoresis, the pattern changed with the molar mixing ratio (TTAB/BPA). At molar mixing ratio 12, for example, zones 1, 2, 3, 4, and 5 were observed. Component 1 is a monomer and component 2 is a dimer of BPA. Components 3–5 are further aggregates of BPA. Thus, the intermolecular SH - SS exchange reaction occurs between BPA molecules unfolded by cationic detergent, leading to the formation of a series of lower aggregates of BPA. Under some conditions, partial precipitation of BPA occurred. Components 1′ and 1″, which are modified monomeis, were observed at certain concentrations of detergent.Studies were also made using a series of cationic detergents differing in the length of hydrocarbon chain C₆C₁₂. Including TTAB, the longer the hydrocarbon chain, the more remarkable was the effect on BPA.The effect of cationic detergent on BPA resembles that of urea insofar as gel electrophoresis is concerned. Furthermore the denatureation of BPA by cationic detergent resembles that by heat and by high pressure. These four agents are initiators of SH - SS exchange reaction for the protein.The effect of cationic detergent differs entirely from that of the anionic detergent such as sodium dodecyl sulfate (SDS). The anionic detergent does not initiate the intermolecular exchange reaction at pH 9.0 even when the molar mixing ratio SDS/BPA is high enough to make BPA unfold.