Glycine-extended processing intermediate of proVIP: a new form of VIP in the rat

The biosynthesis of many peptides including vasoactive intestinal polypeptide (VIP) requires enzymatic alpha-carboxyamidation via a glycine-extended intermediate form. In an effort to identify and quantify glycine-extended VIP in rat tissue extracts a radio-immunoassay specific for this peptide was developed. The concentrations of glycine-extended VIP ranged from 1.3 pmol/g in the brain to 83.9 pmol/g in the small intestine. The identity of the peptide was substantiated by cation-exchange HPLC. The ratio of glycine-extended VIP to amidated VIP varied considerably being highest (63%) in the small intestine. The natural occurrence of glycine-extended VIP in connection with our recent demonstration of its biological activity suggest a physiological role for this biosynthetic intermediate VIP form.