Evidence for presence of peptide alpha-amidating activity in pancreatic islets from newborn rats

The peptide alpha-amidating activity of a homogenate of pancreatic islets from 5-7-day-old rats was investigated, using as substrate a glycine-extended tripeptide (D-Tyr-Val-Gly). The islet homogenates had a marked amidating activity, with a Km of 57 microM, a Vmax. of 185 pmol/h per mg and a pH optimum of 7.0. This activity was dependent on the presence of ascorbic acid (in the reduced form) and Cu2+, the optimum concentrations being 4 mM and 40 microM respectively. On fractionation of the homogenate, the highest specific activity was found in the soluble fraction. Exocrine pancreatic tissue showed very low levels of amidating activity.