Insulin half life and the formation and characterization of the insulin-binding antibodies have been studied in the guinea pig both in vivo and in vitro. The antigen-antibody complexes have also been studied utilizing cellulose column electrophoresis and Sephadex G-200 column filtration. In addition, a quantitative assay procedure for insulin-binding antibodies has been employed.

In normal guinea pigs the injected insulin-I-125 is carried by at least two serum proteins, presumably albumin and an α. globulin, or more specifically 4.5S and 19S proteins. In immune animals the insulin-antibody complexes are represented by a single peak in the (β-γ globulin region on column electrophoresis; they are distinguishable from the uncomplexed antibodies which are 7S γ1 and 7S γ1 globulins. The precipitating insulin antibody also appears to be a 7S globulin. Moreover, the insulin-antibody complexes occur as a single component in the 19S fraction on Sephadex G-200 filtration, and if the complex were a single molecule it would have a molecular weight equivalent of about 630,000.

During the immunization process the insulin binding antibody titer increases progressively in association with an elevation of 7S globulin. In most animals during the early stages of immunization the molecular weight of the antibodies appears to be exclusively of the 7S globulin type; however, in two of seven animals there was, in addition, a small amount of insulin antibody of 19S globulin type early during the immunization period.

The purpose in estimating a molecular weight equivalent of the insulin-antibody complex relates to the possibility that the distinctive features of the angiopathies of diabetes may depend upon certain physicochemical characteristics of this complex.

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