THE DISSOCIATION OF α- AND β-LIPOVITELLIN IN AQUEOUS SOLUTION: PART II. INFLUENCE OF PROTEIN PHOSPHATE GROUPS, SULPHYDRYL GROUPS, AND RELATED FACTORS

Abstract

Removal of protein phosphate groups from α- and β-lipovitellin by means of a phosphatase has shown that these groups do not take part in the dissociation–association process. They appear, however, to be responsible for a difference in their ease of complex formation with calcium ions, and also for their different chromatographic behavior on columns of hydroxyapatite.Both lipovitellins contain about 26 μmoles/g of sulphydryl groups. Sulphydryl group reagents had no effect on the dissociation of α-lipovitellin but markedly changed the behavior of β-lipovitellin. N-Ethylmaleimide and p-chloromercuribenzoate displaced the equilibrium towards the associated form at all pH values below pH 10, but iodoacetamide tended to stabilize the dissociated form against pH changes. The different behavior of these reagents indicates that the sulphydryl groups are not directly involved in the dissociation but their substitution probably causes other changes in β-lipovitellin that affect its dissociation.