[38] Immobilized proteins in single crystals

This chapter describes the technique of immobilizing single protein crystals, presents data on the properties of such crystals, and discusses the uses of insolubilized protein crystals in X-ray diffraction analysis and in studies of the physicochemical properties of enzymes in the solid state. It is suggested that insolubilization of protein crystals could be easily accomplished because the molecules within a crystal are ordered in three dimensions and any reactive amino acid side chain between molecules, which would be few, would be effectively juxtaposed for cross-linking with bifunctional reagents. X-ray structure analysis of a number of proteins indicates that only a few polar side chains (i.e., lysine) at the surface of protein molecule would have any appreciable flexibility in the crystalline state. Crystallographic analysis of glutaraldehyde-treated carboxypeptidase Aα-crystals indicates that intermolecular cross-links are most likely found between lysine residues of different molecule and are few in number.