title: Hypothalamic peptidyl-glycine alpha-amidating monooxygenase: preliminary characterization.
abstract: An enzymatic activity capable of converting mono-[125I]-D-Tyr-Val-Gly into mono-[125I]-D-Tyr-Val-NH2 was identified in a crude mitochondrial/synaptosomal preparation from rat hypothalamus. Further subcellular fractionation studies localized a majority of this enzymatic activity to fractions enriched in synaptic vesicles. The alpha-amidation activity demonstrated optimal activity at pH 7.5 to 8, was stimulated by the presence of copper ions and reduced ascorbate and required the presence of molecular oxygen. Endogenous alpha-amidation activity was inhibited by the addition of ascorbate oxidase. Kinetic analyses demonstrated Michaelis-Menten type kinetics for D-Tyr-Val-Gly as the varied substrate with the values of Km and Vmax increasing as the ascorbate concentration in the reaction increased. A variety of peptides possessing carboxyl-terminal glycine residues were potent inhibitors of the reaction, while peptides lacking a carboxyl-terminal glycine residue were not, suggesting that many glycine-extended peptides may serve as substrates in the alpha-amidation reaction. The characteristics of hypothalamic alpha-amidation activity are similar to those previously reported for the alpha-amidation activity in rat pituitary and mouse corticotropic tumor cells suggesting the presence of closely related enzymes in these tissues.
mesh_terms: D000818:Animals; D055598:Chemical Phenomena; D002621:Chemistry; D003300:Copper; D007031:Hypothalamus / Q000032:analysis / Q000201:enzymology*; D007700:Kinetics; D008297:Male; D006899:Mixed Function Oxygenases; D009097:Multienzyme Complexes; D000587:Oxidoreductases Acting on CH-NH Group Donors / Q000378:metabolism*; D010100:Oxygen / Q000502:physiology; D051381:Rats; D011919:Rats, Inbred Strains; D013572:Synaptic Vesicles / Q000378:metabolism; D014020:Tissue Extracts / Q000378:metabolism
chemical_list: D009097:Multienzyme Complexes; D014020:Tissue Extracts; D003300:Copper; D006899:Mixed Function Oxygenases; C035189:peptidylglycine monooxygenase; D000587:Oxidoreductases Acting on CH-NH Group Donors; D010100:Oxygen