Studies by Small-Angle X-Ray Scattering of the Quaternary Structure of Dissociation Products of the beta-Haemocyanin of Helix pomatia

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Abstract
H. pomatia .beta.-hemocyanin was split into dissociation products by varying pH and the ionic strength. The purity of the solution was checked in an ultracentrifuge. Two defined dissociation products were studied in solution by small-angle X-ray scattering. In Tris .cntdot. HCl buffer, pH 8.0 and ionic strength 1 M, the parameters of the dissociation product (tenths) were determined: MW = 7 .times. 105, volume = 1350 nm3 radius of gyration = 9.0 nm, maximal distance = 28.3 nm, radius of the spherical subunits .apprx. 2.6 nm and number of the subunits .apprx. 19. Tris .cntdot. HCl buffer, pH 8.7 and ionic strength 0.01 M, yielded dissociation products (twentieths) with the parameters: MW = 3.5 .times. 105, volume = 635 nm3, radius of gyration = 7.5 nm, maximal distance = 21.9 nm and radius of the spherical subunits .apprx. 2.5 nm. Assuming that the larger fragment was double the smaller one and using the latest biochemical and morphological results, theoretical scattering curves of models were calculated and compared with the experimental curves. Two models are suggested which agree well with the dissociation products in radius of gyration and scattering.