Rheological and small-angle X-ray scattering investigations on the shape and ordered arrangement of native ovalbumin molecules in aqueous colloids

Abstract

The molecular shape and dispersing state of native ovalbumin molecules in 20 mmol dm^–3 sodium phosphate buffer solution have been studied by small-angle X-ray scattering (SAXS) and a rheological method. The ovalbumin employed is electrophoretically pure and the molecular weight obtained by SDS–polyacrylamide gel electrophoresis and light scattering is ca. 4.4 × 10⁴. The native ovalbumin colloid behaves as a typical non-Newtonian, viscoelastic material above a concentration of several per cent, i.e. it shows apparent yield stress and a certain rigidity. The native ovalbumin molecule is almost spherical, with a radius of ca. 25.2 Å; it disperses individually in very dilute aqueous systems at concentrations of 10^–4–10^–3 g cm^–3 and disperses as a dimeric ovalbumin at higher concentrations. The scattering intensity in SAXS measurement has no peak in the concentration region where the colloidal system is Newtonian; however, the scattering intensity has a broad peak at higher concentrations where the system is non-Newtonian. These SAXS and rheological data suggest that the native ovalbumin molecules disperse, retaining a somewhat ordered arrangement in the concentrated aqueous colloid.