The Interaction of a Cationic Detergent with Bovine Serum Albumin and Other Proteins

Abstract

The binding of tetradecyltrimethylammonium chloride to bovine serum albumin and several other globular proteins was measured, and the resulting conformational changes were studied by optical and hydrodynamic techniques. Native serum albumin was found to have four discrete binding sites for the detergent, to which binding occurs without conformational change, and with a much lower binding constant than for anionic detergents with alkyl chains of similar length. At higher detergent concentrations the cationic detergent resembles sodium dodecyl sulfate, binding cooperatively to serum albumin and to all other proteins studied, with accompanying gross denaturation to form extended rod-like complexes. However, this cooperative process occurs for the cationic detergent at a 10-fold higher concentration than is required for sodium dodecyl sulfate, with the result that completion of the transition was prevented (under the conditions used) by the onset of micelle formation. A possible explanation is offered for this difference, which probably applies to all cationic detergents. The results suggest that cationic detergents are not suitable as substitutes for sodium dodecyl sulfate in procedures in which the denaturing action of the detergent is an essential feature, as, for example, in the determination of molecular weight by gel chromatography or gel electrophoresis.