Glycine-directed peptide amidation: presence in rat brain of two enzymes that convert p-Glu-His-Pro-Gly-OH into p-Glu-His-Pro-NH2 (thyrotropin-releasing hormone).

Abstract
To study the possibility of glycine-directed amidation in rat brain, the substrate p-Glu-His-Pro-Gly-OH was synthesized. Adult and neonatal rat brain and adult rat pituitary were sonicated, forzen and thawed and fractionated by gel permeation chromatography, and fractions from each tissue were assayed for enzymatic activity capable of converting this model substrate into TRH. The presence in rat brain and rat pituitary of 2 enzymes catalyzing conversion of p-Glu-His-Pro-Gly-OH into TRH is reported. Based on the differing chemical and physical properties of these 2 enzymes and their differing affinities for a number of p-Glu-His-Pro-aa-OH analogs (in which aa = glycine, .beta.-alanine, .gamma.-butyric acid and .delta.-aminovaleric acid), there are 2 distinct enzymatic processes for the terminal amidation of peptides in brain and COOH-terminal extensions other than glycine are capable of directing COOH-terminal amidation.