Peptide amidation: evidence for multiple molecular forms of the amidating enzyme.
Amidating enzyme extracted from porcine pituitary was separated into glycosylated and non-glycosylated forms by fractionation on a column of Concanavalin-A Sepharose. The molecular weights of the species present were assessed by HPLC gel exclusion chromatography, which demonstrated that both the glycosylated and the non-glycosylated forms of the enzyme comprise multiple components. The apparent molecular weights of the non-glycosylated forms ranged from approximately 35 kDa to 100 kDa; the glycosylated enzyme contained species with molecular weights ranging from 65 kDa to 135 kDa. Similar proportions of glycosylated to non-glycosylated enzyme (approximately 1:4) were found in the anterior and posterior regions of the pituitary; higher proportions (approximately 1:1) were observed in the thyroid, adrenals and pancreas. The glycosylated forms of the amidating enzyme were shown to exhibit the same mandatory requirement for copper as the non-glycosylated forms, and no differences were seen in respect of their stimulation by dopamine or their pH optima. Both forms catalysed the hydroxylation of glyoxylic acid phenylhydrazone, indicating a common mechanism of action. By these criteria, glycosylation does not affect the activity of the amidating enzyme.
Bradbury
A F
AF
National Institute for Medical Research, Mill Hill, London, United Kingdom.
Smyth
D G
DG
D000818:Animals; D002846:Chromatography, Affinity; D006031:Glycosylation; D007700:Kinetics; D006899:Mixed Function Oxygenases; D008970:Molecular Weight; D009097:Multienzyme Complexes; D000587:Oxidoreductases Acting on CH-NH Group Donors / Q000302:isolation & purification / Q000378:metabolism*; D010902:Pituitary Gland / Q000201:enzymology*; D013552:Swine
D009097:Multienzyme Complexes; D006899:Mixed Function Oxygenases; C035189:peptidylglycine monooxygenase; D000587:Oxidoreductases Acting on CH-NH Group Donors