KINETIC EVIDENCE FOR PROTEIN CLUSTERING AT A SURFACE

The molecules designated 1A2 and 2B4 belong to the cytochrome P450 protein superfamily. They can interact specifically with lipid bilayers via the penetration of part of their amino acid chains into the bilayer. The kinetics of their irreversible adsorption from solution to phospholipid bilayers, accurately measured in the low to intermediate coverage range using an integrated optics reflectance technique, differ significantly: at intermediate bulk solution concentrations, 2B4 shows typical random sequential adsorption (RSA) kinetics, whereas 1A2 shows Langmuir kinetics. At higher bulk concentration the behavior of 1A2 switches to RSA kinetics, and at very low concentrations 2B4 switches to Langmuir kinetics. The Langmuir kinetics provides strong evidence for clustering of the molecules at the bilayer surface, and the observed concentration dependence of the kinetics is consistent with the clusters arising through lateral diffusion of the proteins on the surface. © 1994 The American Physical Society.