Studies of the in vitro human plasma degradation of methionine-enkephalin.
1. Incubation of [3H]tyrosine methionine-enkephalin (6 x 10(-9) M final concentration) with human platelet-poor plasma (1:9 ratio to Trizma Base buffer, pH 7.4) results mostly (greater than 95%) in hydrolysis of the tyrosyl-glycine peptide bond. This enzymatic reaction is essentially completed within 90 min, showing a half-life, Km and Vmax of 12.8 +/- 2.5 min, 0.70 +/- 0.01 mM and 17.90 +/- 1.05 mumol/L/min, respectively. These values are comparable to those previously reported for the human plasma degradation of leucine-enkephalin. 2. As expected hydrolysis of the methionine-enkephalin tyrosyl-glycine peptide bond was blocked by the known aminopeptidase inhibitors bestatin and puromycin (IC50 1.2 +/- 0.4 and 4.3 +/- 2.4 microM, respectively) but not by either thiorphan or captopril. 3. Neither the storing (up to 60 days) nor the freezing and thawing (up to ten times during a 60 days periods) significantly changed the above kinetic parameters, showing the stability of the plasma methionine-enkephalin degrading aminopeptidase.
Mosnaim
A D
AD
University of Health Sciences/The Chicago Medical School, North Chicago Veterans Administration, IL.
Puente
J
J
Wolf
M E
ME
Callaghan
O H
OH
Busch
R
R
Diamond
S
S
D002855:Chromatography, Thin Layer; D004744:Enkephalin, Methionine / Q000097:blood* / Q000493:pharmacokinetics; D006801:Humans; D007930:Leucine / Q000031:analogs & derivatives / Q000494:pharmacology; D011691:Puromycin / Q000494:pharmacology
D011691:Puromycin; D004744:Enkephalin, Methionine; D007930:Leucine; C012211:ubenimex