Protein-Ionic Detergent Interaction

Abstract

Abstract The volume effects produced by the reaction of sodium dodecyl sulfate with bovine serum albumin were determined dilatometrically at 30.0 ± 0.001°. The calculated volume isotherms indicate the operation of at least two major processes: (a) a volume decrease which is caused by a high affinity protein-detergent interaction and occurs at detergent concentrations ranging from 0.02 to 0.08 m; and (b) a volume increase which occurs at SDS concentrations g0.08 m and is attributed to detergent interaction with the structurally altered protein. At detergent concentrations less than 0.02 m either positive or negative volume changes are produced depending on the type and ionic charge of the protein. The effect of pH was investigated by comparing the volume isotherms produced by albumin at pH 5.1 and at pH 8; the negatively charged albumin exhibited a more pronounced volume decrease compared with the isoionic albumin. The volume isotherms are a unique function of the composition, structural organization, and charge of the protein. Acrylamide gel electrophoretic studies of these systems reveal the generation of at least two categories of protein-detergent complexes. At low ratios of sodium dodecyl sulfate (SDS) to protein, there is a progressive increase of the mobility of protein complexes with increasing anion concentration. At detergent concentration ≥0.02 m another component is formed whose mobility is substantially faster than that observed at lower concentrations. At SDS concentrations ≥0.08 m this is the only component present; the mobility of this component is invariant in the concentration region of 0.02 to 0.5 m SDS.