Small-angle X-ray scattering studies of 1-10-size and 1-20-size molecules of Helix pomatia alpha-hemocyanin.

The small-angle X-ray scattering of 1/10-size molecules (in 0.1 ionic strength Tris buffer pH 8.1) and 1/20-size molecules (in 0.1 ionic strength ethanolamine buffer pH 10.6) of a-hemocyanin of the snail Helix pomatia was studied. The radii of gyration, 8.7 nm and 8.0 nm for 1/10-size and 1/20-size molecules respectively, and the shape of the scattering curves indicate that both have a very anisotropic shape. Comparison of the experimental scattering curve of 1/10-size molecules with theoretical scattering curves gives the best agreement for flat cylinders or quadratic prisms the diameter respectively side of which is about 10 times larger than the height (dimensions side = 21 nm, height 2nm ). The scattering curves of various models composed of larger and smaller subunits were calculated; the best agree­ ment was found also for flat models of similar dimensions.