Tissue specific processing of proglucagon. In the pancreatic α-cell, proglucagon is processed by PC2 activity into GRPP, glucagon, major proglucagon fragment (MPGF). In the L-cells, proglucagon is processed by PC1/3 into GLP-1 (7-36NH2) GLP-2 and glicentin. By further PC1/3 activity, glicentin can then be further cleaved into glicentin related pancreatic polypeptide (GRPP) and oxyntomodulin. N-terminal elongated glucagon has also been reported and is termed intestinal glucagon or enteroglucagon. Black arrowheads refer to side-viewing proglucagon antibodies, red arrowheads refer to N-terminal glucagon/oxyntomodulin antibodies and blue arrowheads refer to C-terminal glucagon antibodies. Glucagon measurement should therefore be carried out using, preferably a sandwich ELISA employing N and C-terminal glucagon antibodies. Assay only using black, blue or red antibodies (as depicted here) may over or underestimate glucagon levels due to cross-reactivity with other proglucagon molecules such as glicentin, oxyntomodulin or enteroglucagon 1-61.
Leave a Reply