A non-receptor-type protein phosphotyrosine phosphatase is enriched in secretory vesicles of glucagon - and pancreatic polypeptide - secreting cells of the endocrine pancreas

The secretory vesicles of some cells of the islets of Langerhans of the pan creas contain high amounts of immunoreactive tyrosine phosphatase of the PT P1B/TCPTP subfamily. The cells are located in the peripheral parts of the i slets and were identified as glucagon- and pancreatic polypeptide-forming c ells. The tyrosine phosphatase is also enriched in some of the somatostatin -producing cells but is not elevated either in insulin-producing B-cells or in the exocrine pancreas. Virtually the same patterns were found in pancre tic tissues of rats, guinea pigs, pigs, and mice. High levels of detergent- soluble tyrosine phosphatase were measured in the particular fraction of pa ncreatic islets with a substrate preferred by PTP1B/TCPTP-type protein tyro sine phosphatases.