Abstract
Abstract
Historical Background. Of the four recognized peptide hormones secreted by the endocrine pancreas, pancreatic polypeptide (PP) was the third to be discovered, isolated, and characterized. Insulin (1921-22) and glucagon (1923) preceded and somatostatin (1975) followed the isolation of PP in 1968. Despite this sequence of events—and the time interval since its discovery—PP remains somewhat of an enigma both in name and in function. The reluctance to label this polypeptide with a more descriptive title than the lackluster PP it bears stems largely from the fact that while broad actions may be attributed to it, no outstanding or dominating effect has been identified with its actions. Thus, the only characteristic carried by use of the phrase PP is to signify the species of PP one is discussing, such as avian, bovine, rat, porcine, ovine, and human, for example. The avian structure has 15 identities (of a total of 36) with that of bovine PP, and the latter differs by one or two residues from most other mammalian PP at any of three or four positions within the molecule. Thus, strong structural conservatism exists from an evolutionary point of view.
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