Pancreatic polypeptide, a 36-amino acid peptide with a molecular weight of 4250, was first isolated from chicken pancreas (Kimmel et al. 1971) and named avian pancreatic polypeptide (aPP). Subsequent preparations of the homologous hormone from bovine and human pancreas were termed bPP and hPP, respectively. With the exception of two teleosts, Dicentrarchus labrax (Thorpe and Duve 1985), and Oncorhynchus kisutch (Kimmel et al, manuscript), PP has not been detected by RIA in islets below the amphibians (Greeley et al. 1984). Immunohistological findings suggest that it occurs in the pancreas of all vertebrates above the cyclostomes (see Chap. 4.2). In their report on the primary structure of rat PP, Kimmel et al. (1984) compiled the sequences of nine PPs, from mammals, birds, and reptiles. Of the 36 amino acids, 10 are invariant, the lowest percentage of invariant residues among the four major islet hormones (Table 12.1). Additional sequence changes might then be expected in amphibian and fish PPs. Indeed, in a recent study Kimmel and coworkers (manuscript) report that the salmon pancreas contains a 36-residue peptide that is more homologous with porcine NPY (83%) and PYY (75%) than any of the previously characterized pancreatic peptides; and they mention a similar peptide also for Lepisosteus spatula (see below). Another homolog of PP, peptide YG, was recently identified in the PP cells of the islets of the anglerfish by Noe et al. (1986). Compared with hPP, the sequence variations of the different PPs range from two amino acids in the dog and pig to 23 in the goose.
KeywordsGlycerol Manifold Carbohydrate Tyrosine Arginine
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