Gastrin-amidating enzyme in the porcine pituitary and antrum. Characterization of molecular forms and substrate specificity.

摘要: Abstract As is the case with many other peptide hormones of brain and intestine, formation biologically active gastrin from a glycine-extended processing intermediate occurs via action peptidylglycyl alpha-amidating monooxygenase (PAM). The observation that exists primarily as unamidated precursors in pituitary but amidated antrum prompted this study to examine whether amidating enzymes two organs were different their characteristics. Amidating activity was quantified by measuring conversion tridecagastrin (G13-Gly) hexapancreatic polypeptide (PP6-Gly) radio-immunoassay. Two molecular forms identified both porcine pituitary. first, PAM-A, had an apparent Mr 51,000 net negative charge at pH 7.0, whereas PAM-B smaller (Mr approximately 30,000) positive 7.0. Both similar cofactor requirements (copper, ascorbic acid, catalase) optima Km significantly lower Vmax higher for PP6-Gly than G13-Gly antrum. These data suggest although there no difference between antral PAM, selective affinity PAM certain substrates may provide mechanism differential amidation within given tissue or cell.