Effects of detergent micelles on the recombination reaction of opsin and 11-cis-retinal.

When detergent-solubilized proteins interact with hydrophobic or amphiphilic molecules in the presence of detergent micelles, the solubility of the latter species in the micelles must be included in both thermodynamic and kinetic treatments. In this paper, we derive equations which describe the distribution of species present at equilibrium for a system in which a detergent-solubilized protein binds a hydrophobic (or amphiphilic) ligand. We have applied the formalism developed in this paper to the reaction describing the formation of rhodopsin from its apoprotein and 11-cis-retinal. Qualitatively, the results demonstrate that a significant portion of the observed decrease in the extent of recombination for rhodopsin solubilized in either sodium cholate or Tween 80 may be attributed to the partition of retinal into detergent micelles and that a detergent-induced protein denaturation need not be invoked to explain the data. We also discuss results for rhodopsin solubilized in a nonionic detergent (octaethylene glycol n-dodecyl ether) in which the detergent is clearly causing irreversible loss of the capability to recombine with 11-cis-retinal.