Hydrophile-lipophile balance and critical micelle concentration as key factors influencing surfactant disruption of mitochondrial membranes.

A systematic approach to selection of surfactants for disrupting biological membranes, for solubilizing their components, and for removing the surfactant by dialysis is described. The two relevant surfactant parameters were the critical micelle concentration (CMC) and the hydrophile-lipophile balance (HLB). Rat liver mitochondria were treated with two series of nonionic surfactants and the extent of extraction of total protein, total lipid, and six enzymes was determined. Within the homologous series of Triton surfactants, maximum protein and phospholipid extraction occurred at HLB values between 12.5 and 13.5. In addition, a single surfactant species solubilized more protein than a mixture of surfactants with the same mean HLB value. In order to examine independently the effect of CMC and HLB on protein extraction, a specialty surfactant, S10-7, was prepared and compared with its structurally similar analog, Brij 56. Above a concentration of 0.35%, both Brij 56 and S10-7 extracted about 70% of the mitochondrial protein. Hence, for optimum extraction of mitochondrial protein and lipids the HLB must be about 13, and the surfactant concentration must be above the CMC. The S10-7 dialyzed almost as rapidly as cholate and far more rapidly than Brij 58 and Triton X-100. It therefore possesses the two most desirable surfactant properties for disruption of membranes, a high CMC for rapid dialysis, and an HLB value of 13.2.