[Isolation and study of the properties of an insulin-binding protein from the blood serum].

A question of the existence of blood proteins binding unmodified insulin has remained open for many years. This paper is devoted to the description of a method of isolation and characteristics of the insulin-binding protein (IBP) isolated from rat and human blood sera. The level of IBP in the serum was 0.12-0.15 mg/ml. The protein was referred to IgG basing on the data of electrophoresis under denaturing conditions, immunoelectrophoresis and immunoenzymatic analysis. The constant of protein association with insulin varied with regard to a source within 1.5.10(-7) to 2.5.10(7) M-1. The studied protein bound both 125I-modified and unmodified insulin preparations. The calculation based on IBP parameters, showed that no less than half of the blood insulin must be in a bound condition. The capacity of such insulin-binding system is rather great and is capable of leveling down sharp changes in a blood insulin concentration.