Effects of zinc ion on the conformation of antigenic determinants on insulin

Abstract

Comparison of c.d. spectra of Zn-insulin with Zn2+-free insulin demonstrated significant differences. It has been proposed that these differences are due to either changes in the structure of insulin monomers within aggregated insulins or the results of insulin aggregation. The effect of Zn2+ on the immunological activity of insulin indicated that the antigenic determinants of insulin were also altered. The apparent loss of immunological activity of monoiodotyrosylinsulin was demonstrated to be due to the loss of Zn2+ rather than the substitution of iodine. The immunological activity of Zn-insulin and Zn2+-free insulin was compared in both the radioimmune and immune haemolysis-inhibition assays by using an identical population of antibodies and concentrations of inhibitor. Relative to Zn-insulin, Zn2+-free insulin had a markedly attenuated immunological activity in the immune haemolysis-inhibition assay, whereas in the radioimmune assay slightly greater immunological activity was observed with the Zn2+-free insulin. These observations are submitted as evidence that the removal of Zn2+ perturbs the conformation of determinants that react with antibodies operative in the immune haemolysis-inhibition assay (immune haemolysis determinants) and has a minimal effect on the conformation of determinants that react with antibodies operative in the radioimmune assay (radioimmune determinants).

Recognition of human insulin in vitro by T cells from subjects treated with animal insulins.

“…Furthermore, kinetics and ion concentration required for mitogenic responses to free zinc are different than the response to insulin (30 and unpublished observations). Antibody studies also support the concept that immunoreactive determinants on the molecules are present in zinc-dependent conformations (31,32). In studies with insulin antisera not only was zinc-free insulin shown to have marked decreased immunologic activity at concentrations where insulin was thought to be monomeric (31), but it was also shown that addition of zinc restored immunologic activity (32).…”

“…Antibody studies also support the concept that immunoreactive determinants on the molecules are present in zinc-dependent conformations (31,32). In studies with insulin antisera not only was zinc-free insulin shown to have marked decreased immunologic activity at concentrations where insulin was thought to be monomeric (31), but it was also shown that addition of zinc restored immunologic activity (32). Recognition of similar zinc-dependent immunogenic determinants by human lymphocytes is one potential explanation for the extensive cross-reactivity between human and animal insulins.…”

Zinc Status among Type (2) Diabetes Mellitus in the State of Qatar

“…Structurally, the addition of zinc to insulin results in conformational changes, which have been detected by ultraviolet circular dichoric spectroscopy [38]. It has been reported that the removal of zinc alters the ternary structure of insulin and can reduce the immunological insulin activity due to the changes in antigenic determinations of insulin [39,40]. The zinc contents of diabetic pancreases have been reported to be depressed when compared to normal ones [41], and diabetic children have been shown to have low hair zinc levels, which return to normal after insulin administration [42].…”

A zinc-dependent epitope on the molecule of thymulin, a thymic hormone.

“…Other antibodies, such as the MA-FTS monoclonal antibody or some of the antibodies contained in the rabbit polyclonal antithymulin antiserum, produced against synthetic thymulin and screened by ELISA or RIA, recognize the peptide independently of the presence of zinc. Interestingly, the existence of zinc-dependent antigenic determinants has also been suggested for insulin (16). A metal-dependent epitope has also been reported for the prothrombin molecule (17).…”