[Heterogeneity of the immunoreactivity of A14, A19, B16 and B26- (125I) monoiodoinsulin to different species of anti-insulin immuno sera]

Abstract

By using lactoperoxidase oxidation with 6 mol. urea in the reaction medium, the four tyrosine residues contained in insulin molecule were iodinated as monoiodoinsulins. These tracers, namely A14, A19, B16 and B26- (125I) monoiodoinsulins were separated with polyacrylamide gel electrophoresis+QAE-Sephadex A25 chromatography. The present study demonstrated that the radiochemical purity of these tracers was high (> 98%) and the specific radioactivity also high. The binding of these tracers to surplus insulin antibody was more than 95%. These our tracers were tested in two RIA systems against 35 species of guinea-pig anti-insulin immuno sera to compare their immunoreactivity (Ka, Scatchard analysis) to each immunoserum. The two RIA systems were antibody dilution and self displacement, and in both of them, only iodinated insulin and insulin antibody were present in the reaction fluid. The results showed that for 16 antiinsulin immuno sera, Ka for A14, A19, B16 or B26-monoiodoinsulin were significantly different, and for the rest 19 immuno sera no significant difference could be detected. The possible mechanism and implication of this phenomenon were discussed.