Shape and Quaternary Structure of a-Globulin from Sesame (Sesamum indicum L.) Seed as Revealed by Small Angle X-ray Scattering and Quasi-elastic Light Scattering

The a-globulin from sesame seed has a molar mass of
2.7 X lo6 g mol", determined by x-ray scattering, and
(2.8 f 0.3) lo6 g mol", determined by quasi-elastic
light scattering. The radius of gyration Rc amounts to
(4.1 2 0.1) nm and (3.9 f 0.2) nm as determined by
Guinier approximation and from the distribution func-
tion I)(x), respectively. The molecule has a Stokes
radius& of (5.4 20.15) nm and a maximum dimension
L of (11 e L e 15) nm. The translational diffusion
coefficient D&,, and the ratio of frictional coefficients
f / f m i . amount to (3.95 2 0.12) X 10" om2 s" and 1.25,
respectively. The quaternary structure of the protein
molecule is approximated by a model consisting of six
spherical subunits situated at the vertices of an octa-
hedron having the symmetry 32.