A NEUTRON REFLECTIVITY STUDY OF A SPREAD MONOLAYER OF BOVINE SERUM-ALBUMIN

Neutron reflectivity profiles were obtained for spread layers of the protein bovine serum albumin (BSA) at the air/water interface at a surface pressure of 15 mN m-1. By the use of hydrogen-deuterium isotopic substitution in the subphase, and constrained model fitting, the distribution of protein at the interface has been determined. The simplest possible model consistent with the data is a two-layer model. The upper layer contains the major portion of the molecule which lies flat along the surface, consistent with the alpha-helix conformation, and the lower layer contains only 7% vol. of BSA and probably consists of a number of hydrophilic chains dangling down from the upper layer. The results also imply that some 30% wt. of the protein is lost to the subphase on initial spreading.