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Degradation kinetics of leucine5-enkephalin by plasma samples from healthy controls and various patient populations: in vitro drug effects. Am J Ther 2000 May;7(3):185-94 PMID: 11317167

Pubmed ID



Incubation of [3H]tyrosine leucine5-enkephalin with platelet-poor human plasma (final concentration 1 x 10(-8) M; 1:9 ratio to Trizma base buffer, pH 7.4) resulted in rapid and complete peptide degradation in each of the subjects studied, with more than 95% of the initial labeled tyrosine consistently recovered as the free amino acid (< or =30 minutes). Essentially, and irrespective of the incubation time (1-180 minutes), tyrosine was the only Leu metabolite formed; we were unable to identify significant amounts (> or =3%) of any other possible labeled or nonlabeled Leu degradation fragments. Neither gender (64 men and 20 women; samples tested individually), age (men, 23-70; women, 25-65 years), nor the subjects' medical condition appeared to make a significant difference in either the t1/2 of Leu elimination, the initial velocity of this reaction (x +/- SD, median, minimum and maximum of 12.0 +/- 0.9, 12.0, and 10.6-13.7 minutes; 1.2 +/- 0.3, 1.1, and 0.6-2.0 pg/min, respectively), or in the Km and Vmax values for aminopeptidase Leu degradation (x +/- SD; 0.81 +/- 0.01 mM and 14.30 +/- 1.17 micromol/L/min, respectively). Subjects were diagnosed as chronic schizophrenics (n = 15), polydrug abusers including alcohol (n = 9) and polydrug abusers excluding alcohol (n = 8), chronic alcoholics (n = 12), and migraineurs (n = 10) during or outside an acute migraine episode; for comparison we used a group of gender-matched (20 men and 10 women), age-comparable, drug-free, healthy volunteers. Differences in plasma storage time or repeated sample freezing and thawing failed to alter significantly any of these kinetic parameters of Leu metabolism or to change the identity and/or relative ratio of the products formed. The Leu degradation rate was pH and temperature dependent (optimum, 7.4 and 37 degrees C, respectively). Leu degradation was strongly and similarly inhibited by puromycin, bacitracin, and bestatin (IC50 [+/- SD] of 1.4 +/- 0.2 micromol/L) and to a lesser extent by various L-tyrosine-containing Leu fragments. The kinetics of this reaction was not significantly affected by either thiorphan, N-carboxyphenylmethyl leucine, or any other of a number of monoamine neurotransmitters, substances of abuse, nonsteroidal anti-inflammatory agents, and miscellaneous compounds tested (concentration up to 10(-4) mol/L).

Author List

Mosnaim AD, Wolf ME, Nguyen TD, Puente J, Freitag F, Diamond S


Frederick G. Freitag DO Associate Professor in the Neurology department at Medical College of Wisconsin


2-s2.0-0034189812   11 Citations

MESH terms used to index this publication - Major topics in bold

Anti-Inflammatory Agents, Non-Steroidal
Drug Interactions
Enkephalin, Leucine
Middle Aged
Migraine Disorders
Specimen Handling
Substance-Related Disorders
jenkins-FCD Prod-297 dff1a717c492f00bf6291286365f1f4fe95208f1