Fragments of the glucagon molecule have been examined for biological activity. The peptide hormone (amino acid residues 1–29) was cleaved with cyanogen bromide, resulting in fragment 1–27, and with trypsin. These fragments as well as a synthetically prepared fragment, 1–23, and the structurally related (14 out of 27 residues identical) hormone, secretin, were all assayed by measuring their ability to activate rat liver adenyl cyclase. Of the fragments tested, only that resulting from cyanogen bromide cleavage (#1–27) possessed activity. The results indicate that the COOH-terminal portion of the hormone is essential for activity (#1–23 is inactive), but that 2 residues can be cleaved from the COOH-terminal end without complete loss of activity. (Endocrinology85: 638, 1969)
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Spiegel et al. (1969) studied this question.