Partial Purification of an Insulin Inhibitor from Human Albumin Fractions1

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Abstract
Human albumin fractions prepared from normal and diabetic subjects by Debro and Conn fractiona-tion procedures inhibit the action of insulin on rat hemidiaphragm muscle in vitro. By G-100-Sephadex-gel filtration, it has been possible 1) to separate insulin inhibitory activity from the major portion of starting albumin leaving non-inhibitory albumin which appears to be physically and immunologically unaltered, and 2) to concentrate inulin inhibitory activity (Fraction x) 150-fold over the starting preparation (200 [mu]g protein/ml of Fraction x vs. 30,000 [mu]g protein/ml of albumin). The inhibitor, which is presumably bound to albumin in the original preparation, is somehow dissociated from albumin under the conditions of Sephadex filtration and is then separable from albumin on the basis of difference in molecular size. That the inhibitor is a small molecular weight material is supported by its ready dialyzability from solutions containing low concentrations of albumin (.001%). At higher concentrations of albumin (.2-3%), the inhibitor is no longer dialyzable. Further purification of the inhibitor and the mechanism of association and dis-association of inhibitor and albumin are under continuing study.