In secretory granules of intestinal L cells, proglucagon is proteolytically cleaved by prohormone convertase 1 (PC1) at two sites to yield GLP-1 (7-36) or GLP-1 (7-37). In humans almost all circulating GLP-1 is GLP-1 (7-36) amidated at the C-terminus. Experiments in knockout mice have shown that PC1 is necessary for cleavage. Carboxypeptidase E and peptidylglycine alpha-amidating monooxygenase may be involved in trimming and amidating the C-terminus.
Bonic, A, Mackin, RB
serine-type endopeptidase activity of PC1:calcium cofactor [secretory granule lumen]
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