Structural characteristics of a globular protein investigated by X-ray photoelectron spectroscopy: comparison between a legumin film and a powdered legumin.

Films of legumin, a pea protein, were deposited onto a glass support using the Langmuir-Blodgett method, at various surface pressures. XPS study of these films show that their thickness increases with the deposition pressure. At the pressure limits of films stability, the thickness values (respectively 73 and 110 A) are close to the protein dimensions. Layered at low pressure, the oblate protein stands up when pressure increases. Furthermore, XPS study shows that the orientation of the external flexible loops depends on the obtention conditions. Thus, in the case of Langmuir-Blodgett films, hydrophobic residues are turned towards the external surface, and the hydrophilic ones towards the glass substrate. But, in the opposite, when protein is obtained by lyophilization, the hydrophilic residues are orientated outsides. It seems possible to determine by XPS the nature of the residues which give to the protein its reactivity, since they are located at its external surface.