The general aspects of ionic surfactant-protein interaction are primarily introduced. Emphasized are that the surfactant “monomers” bind to protein to form micelle-like aggregates and that the electrostatic interaction of hydrophilic group of the surfactant, which participates in the aggregate formation, with an oppositely charged residue of protein is indispensable in the structural change of protein. Secondarily, structural changes of bovine serum albumin (BSA) and horse myoglobin in thermal denaturations up to 130°C are introduced. The helical structures of these proteins are partially disrupted with rise in temperature above 30°C. However, the structure of BSA, disrupted below 50°C, is reversibly reformed upon cooling to 25°C. Myoglobin shows such a reversibility up to a temperature as high as 75°C. The helicities of BSA and myoglobin sharply decrease beyond these critical temperatures, 50 and 75°C, respectively. On the other hand, the coexistence of sodium dodecyl sulfate (SDS) protects the structures of both the proteins in the thermal denaturations beyond the critical temperatures. The protective effect maximally appears on the BSA structure at extremely low SDS concentrations. This novel function, overlooked in the two-component systems of only surfactant and protein, might be fulfilled by the amphiphilic surfactant ion in a monomer state.

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