Conformational study and determination of the molecular weight of highly charged basic proteins by sedimentation equilibrium and gel electrophoresis

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Abstract
Several highly charged protamines and some related proteins from the sperm of molluscs [Loligo pealei, Gibbula divaricata, Mytilus edulis and Cryptochiton stellerii] were studied. Circular dichroism and hydrodynamic parameters obtained from the sedimentation constant and intrinsic viscosity show that these proteins behave as random coils. It appears that a small amount of structure is present at basic pH. The MW of these proteins is determined by several methods. When sedimentation equilibrium is used, the influence of concentration is much smaller than expected. The highly charged nature of these proteins can be properly taken into account by using the methodology presently available. The calculations were carried out in most cases by the method of Chernyak et Magretova (1975) which does not require the knowledge of the protein concentration. The overall adequacy of this approach was ascertained by using as standards histone H1 and the protamine thynnine, both of known MW and different charge densities. An electrophoretic method for the rapid estimation of the MW of this type of proteins is also given. The values obtained by this method, and those found either with the Scheraga-Mandelkern equation or from the sedimentation and diffusion constants, agree within experimental error with the values obtained from sedimentation equilibrium.

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