Abstract
Although it is now well established that the fully interdigitated phase is induced in saturated like-chain phosphatidylcholines (PCs) by a variety of amphipathic molecules including alcohols, no systematic study of the properties of the inducing molecules has been reported. To elucidate the stereochemical features that lead to the alcohol induction of interdigitation in PCs, we have investigated the induction of interdigitation in distearoylphosphatidylcholine (DSPC) by a series of alcohols. Our previously established DPH (1,6-diphenyl-1,3,5-hexatriene) fluorescence intensity method has been expanded (P. Nambi, E. S. Rowe, and T. M. McIntosh (1988), Biochemistry 27:9175-9182) and used to determine which of the alcohols induce interdigitation and to determine the threshold concentrations for each. We have found that each of the n-alcohols up to heptanol and several branched alcohols are capable of inducing interdigitation in DSPC; octanol and nonanol do not appear to induce interdigitation by these criteria. The threshold concentrations for interdigitation for each of these alcohols up to heptanol were found to be correlated with the membrane: buffer partition coefficients. The mole fraction of bound alcohol at the threshold concentration was similar for each of the alcohols up to pentanol. These results are discussed in terms of a general mechanism of the formation of the interdigitated phase.