Abstract
The degradation of insulin by the enzyme insulin protease and by isolated hepatocytes results in proteolytic cleavages in both the A and B chains of intact insulin. Previous studies have shown that one of the A chain cleavages is between A13 leucine and A14 tyrosine and that a second cleavage occurs carboxyl to the A14 residue. In the present study we have used insulin specifically iodinated on the A19 tyrosine and examined the A chain cleavages by the enzyme and by hepatocytes. Insulin degradation products were purified by HPLC and sequenced by automated Edman degradation. Only two A chain cleavage sites were identified, one the previously reported A13–A14 and the other between A14 tyrosine and A15 glutamine. These data thus identify the second A chain cleavage site and further support the role of insulin protease in hepatic metabolism of insulin.
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