In K cells of the intestine the transcription factors PAX6 and PDX-1 activate transcription of the gene encoding Glucose-dependent Insulinotropic Polypeptide (GIP, first called Gastric Inhibitory Peptide). ProGIP is cleaved in secretory granules by Prohormone Convertase 1 (PC1) at 2 sites to yield mature GIP. In response to fat the GIP is secreted into the bloodstream. The half-life of GIP in the bloodstream is determined by Dipeptidyl Peptidase IV, which cleaves 2 amino acids at the amino terminus of GIP, rendering it biologically inactive.
Kim, W, Egan, JM
Todd, JF, Bloom, SR
Drucker, DJ, Baggio, LL
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