Studies by X‐Ray Small‐Angle Scattering of the Quaternary Structure in Solution of Halves and Tenths of Helix pomatia Haemocyanin and of Sepia officinalis Haemocyanin

Abstract

The haemocyanin of Helix pomatia was dissociated into halves and tenths. Both fragments as well as the haemocyanin of Sepia officinalis were studied in solution by small‐angle X‐ray scattering. A concentration series of halves of the α‐haemocyanin of H. pomatia was studied in 10 mM phosphate buffer, 1 M LiCl at pH 6.25. The solutions were homodisperse and the following data could be determined: radius of gyration = 14.0 nm, molecular weight = 4300000, volume = 8400 nm3, hydration = 0.45 g H2O/g protein, partial specific volume 0.730 ml/g. A model equivalent in scattering is a hollow cylinder with the dimensions: height 18 nm, outer diameter 33 nm and inner diameter 15 nm, composed of nearly spherical subunits (diameter about 4 nm). The solutions of the tenths prepared by ethoxyformylation were not completely homodisperse; therefore only qualitative results (indicating a very anisotropic shape) could be obtained. The haemocyanin of S. officinalis was studied in 0.1 M phosphate buffer, pH 6.0. The data obtained were very similar to those found for the halves of the α‐haemocyanin of H. pomatia: radius of gyration = 14 nm, molecular weight = 4000000, volume = 8000 nm3, hydration = 0.44 g H2O/g protein, partial specific volume 0.736 ml/g. The overall shape and substructure are also nearly identical to those found for the halves of the α‐haemocyanin of H. pomatia. Copyright © 1974, Wiley Blackwell. All rights reserved