Biphasic Interaction of γ-Globulin with Copper Cations

Abstract

Interactions of human serum gamma-globulin with copper cations in solution were studied by differential ultraviolet spectrophotometry. Copper in supraphysiological concentrations increases optical density of protein solution, reflecting the effect of gamma-globulin saturation with metal. In physiological and lower concentrations of copper cations we observed hypochromia in the protein absorption spectrum. Conformational changes in g-globulin molecule during interactions with copper by the surface and intramolecular binding sites and possible role of bivalent metal cations in the maintenance of certain conformations of immunoactive serum proteins are discussed.

Reactions between Human Serum γ-Globulin and Zinc Cations

“…The detected relationship corresponds to that observed in experiments with copper [4]. The effect of zinc was appreciably lower than that of copper: even at the level of the maximum increment in the optical density it reaches only half of the spectral effect induced by the presence of copper [4].…”

“…Spectral changes in γ-globulin solution are less pronounced than in experiments with copper: the increment in optical density in the presence of saturating concentration of zinc is recorded at a 2.0-2.5 times lower level, while the saturating concentration 6 µg/ml is several times higher than that for copper [4]. In contrast to the effects of copper cations, zinc causes no precipitation of γ-globulin agglomerates.…”

“…This concept is based on the data on γ-globulin interactions with copper by the extra-and intraglobular sites and on the possibility of forming surface and internal protein-metal complexes [3,4]. Biphasic nature of the reaction indicates different time of cation saturation of external and internal coordinating sites differing by the parameters of reactions with copper (presumably, by dissociation constant) and retaining certain stability (at least, in local environment) [4].The effects of zinc (in contrast to those of copper, which is not regarded as immunoactive trace element) in immune reactions are well studied. The role of zinc in immunogenesis can be different: it determines biological activity of thymulin [7,8], regulates early stages of T-lymphocyte maturation [14], apoptosis [13,14], plays an important role in the provision of cytokine production and reception [7,14], directly participates in the main immune reactions [8,14].…”

“…This concept is based on the data on γ-globulin interactions with copper by the extra-and intraglobular sites and on the possibility of forming surface and internal protein-metal complexes [3,4]. Biphasic nature of the reaction indicates different time of cation saturation of external and internal coordinating sites differing by the parameters of reactions with copper (presumably, by dissociation constant) and retaining certain stability (at least, in local environment) [4].…”

“…The methodological approaches used in this study correspond to our previous experiments with copper [3,4], which makes possible a comparison of the effects of cations with similar and different properties in the realization of biological activity [1,6,9].…”