Biosynthetic human insulin (BHI) was compared with highly purified human pancreatic and pork insulin with regard to its ability to bind to erythrocytes of normal and insulin-dependent diabetic subjects (type I diabetes). The binding affinity or capacity of erythrocyte from both normal and diabetic subjects were comparable for biosynthetic and pancreatic human insulin. In contrast, binding of pork insulin to erythrocytes was significantly decreased at low insulin concentrations in normal as well as in diabetic subjects due to a reduced receptor affinity. The affinity of the “empty sites” was 5.25 × 10−8 M−1 with pork insulin in normal subjects and 6.1 × 10−8 M−1 in diabetic subjects; with both human insulins, the affinities were 6.9 × 10−8 M−1 in normal subjects and 8.6 × 10−8 M−1 in diabetic subjects. The number of insulin receptors per erythrocyte was calculated as being 30 in normal subjects and 35 in diabetic patients.

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