Characterization of a peptide alpha-amidation activity in human plasma and tissues.
Peptidyl glycine alpha-amidation activity has been detected in human plasma and in several human tissues known to synthesize biologically active alpha-amidated peptides. Activity was monitored by measuring conversion of mono-[125I]-D-Tyr-Val-Gly into mono-[125I]-D-Tyr-Val-NH2. The plasma alpha-amidation activity is dependent on molecular oxygen, copper, and ascorbic acid and appears to recognize a variety of peptide substrates which contain carboxyl terminal glycine residues. Kinetic analyses demonstrated Michaelis-Menten kinetics with a Km of 14 mumol/L for D-Tyr-Val-Gly. Based on gel filtration, the apparent molecular weight of the peptidyl glycine alpha-amidation activity in human serum is 60,000. The level of peptidyl glycine alpha-amidation activity in adult plasma (N = 17) was 106 +/- 3 pmol/mL/h (Mean +/- SEM) with no difference between male and female subjects (range 84 to 126 pmol/mL/h). In subjects under 15 years old (N = 10), mean plasma activity was 128 +/- 10 pmol/mL/h, higher than values for adult control plasma (P less than .05). In serum from hypothyroid adults (N = 13), mean serum activity was 141 +/- 11 pmol/mL/hr, higher than euthyroid controls (P less than .025). The most striking elevations in alpha-amidation activity occurred in plasma from patients with peptide-secreting tumors. Patients with medullary thyroid carcinoma (N = 19) had a mean plasma peptidyl glycine alpha-amidation activity of 142 +/- 52 pmol/mL/h (range 84 to 435 pmol/mL/h). The level of plasma alpha-amidation activity in one patient with metastatic carcinoid tumor was 560 pmol/mL/h.(ABSTRACT TRUNCATED AT 250 WORDS)
D000293:Adolescent; D000328:Adult; D000368:Aged; D001205:Ascorbic Acid / Q000494:pharmacology; D002648:Child; D003300:Copper / Q000502:physiology; D004700:Endocrine System Diseases / Q000201:enzymology; D004789:Enzyme Activation / Q000187:drug effects; D005260:Female; D005998:Glycine / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008297:Male; D008670:Metals / Q000494:pharmacology; D008875:Middle Aged; D006899:Mixed Function Oxygenases; D009097:Multienzyme Complexes; D000587:Oxidoreductases Acting on CH-NH Group Donors / Q000097:blood / Q000378:metabolism*; D010100:Oxygen / Q000502:physiology; D010455:Peptides / Q000378:metabolism*
D008670:Metals; D009097:Multienzyme Complexes; D010455:Peptides; D003300:Copper; D006899:Mixed Function Oxygenases; C035189:peptidylglycine monooxygenase; D000587:Oxidoreductases Acting on CH-NH Group Donors; D001205:Ascorbic Acid; D010100:Oxygen; D005998:Glycine