The effects of diverse proteins on the solubilization of various hydrophobic probes by protein.detergent complexes

The solubilization behavior of various protein.detergent complexes with respect to a particular water-insoluble organic substance ("hydrophobic probe") dimethylaminoazobenzene, was reported in earlier studies. The present report describes further the solubilization of other hydrophobic probes (e.g. Sudan II, naphthalene, anthracene and azobenzene) in various protein.sodium dodecyl sulfate complexes, in order to enlarge the scope of our understanding of these phenomena, which undoubtedly play a part in the transport of different water-insoluble organic substances in the living organisms. Solubilization by the various protein.SDS complexes is found to be specific for each probe. The amount of a particular probe solubilized is nearly always equal to the amounts which are solubilized by pure SDS micelles equivalent in amount to the SDS bound. Serious exceptions are found with two heme proteins (e.g. myoglobin and hemoglobin) and a few others. The hemeprotein.SDS complexes also exhibit regions of flat plateaus in the solubilization curves, whereas the binding equilibria show progressively larger amounts of SDS bound. The solubilization of probes by cationic detergent (cetylpyridinium chloride and cetyltrimethylammonium bromde).protein complexes indicate that the solubilization phenomena are related to the environment of the binding sites (the cationic detergents are known to bind at different sites on the protein than the anionic detergents, i.e. SDS in the present case). With anionic detergents the effective chain length of the pseudo-micellar protein.detergent clusters is sufficient to cause an increase in solubilizing effectiveness of about 1.5 between the complexes and pure micelles. When small probes such as naphthalene are used such ratios are found. With larger probes the effectiveness ratio is reduced to 1.0 or even less as a result of steric interference with the formation of the protein.detergent.probe clusters. The solubilization energy exhibited by each protein.detergent complex is largely determined by the individual protein, and by the charge on the detergent.