STRUCTURAL CHARACTERISTICS OF A GLOBULAR PROTEIN INVESTIGATED BY X-RAY PHOTOELECTRON-SPECTROSCOPY - COMPARISON BETWEEN A LEGUMIN FILM AND APOWDERED LEGUMIN

Films of legumin, a pea protein, were deposited onto a glass support u sing the Langmuir-Blodgett method, at various surface pressures. XPS s tudy of these films shows that their thickness increases with the depo sition pressure. At the pressure limits of films stability, the thickn ess values (respectively 73 and 110 Angstrom) are close to the protein dimensions. Layered at low pressure, the oblate protein stands up whe n pressure increases. Furthermore, XPS study shows that the orientatio n 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 b y lyophilization, the hydrophilic residues are orientated outsides. It seems possible to determine by XPS the nature of the residues which g ive to the protein its reactivity, since they are located at its exter nal surface.