Proinsulin Content of Adult and Fetal Pancreatic Tissue Extracted after Rapid Freezing in Situ

The proinsulin and insulin content of fetal and adult porcine pancreas and adult rabbit pancreas were determined after the tissues were rapidly frozen in situ to prevent protein degradation. Proinsulin was found to constitute 2-3% of the total immunoreactive insulin. The cross-reactivity of porcine proinsulin to porcine insulin antibody was 33% that of insulin, so that the proinsulin content of porcine pancreas on a molar basis is approximately 7%. These results demonstrate that proinsulin does not represent a major storage form of insulin in either adult or fetal pancreas.