ISSN:
1471-4159
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Medicine
Notes:
Abstract: Incubation of β-endorphin with cytosolic and particulate fractions of rat brain resulted in the formation of several peptides, including γ-endorphin [β-endorphin-(1–17)] and β-endorphin-(18–31), indicating the presence of enzyme activity cleaving the Leu17-Phe18 bond of β-endorphin. An assay for this Leu-Phe cleaving activity, based on the cleavage of the 14C-labeled substrate acetyl-Val-Thr-Leu-Phe-[ε ([14C]CH3)2]Lys-NHCH3, was used to examine the properties of this enzyme activity. β-Endorphin-(1–31) competitively inhibited the Leu-Phe-cleaving enzyme activity on the pentapeptide substrate. Over 90% of activity was recovered in the cytosolic fraction. Leu-Phe-cleaving activity behaved like a thiol endopeptidase because it was inhibited by low concentrations of N-ethylmaleimide, p-chloromercuribenzoate, p-chloromercuribenzoyl sulfate, and low concentrations of Hg2+. Low concentrations of sulfhydryl compounds stimulated Leu-Phe-cleaving activity. The activity was optimal between pH 8.5 and 9.0. The Km of Leu-Phe-cleaving activity in the cytosolic fraction was 35 μM and in the particulate fraction 88 μM with Vmax values of 193 and 15 nmol mg protein−1 h−1, respectively. The apparent molecular mass of the Leu-Phe-cleaving enzyme was estimated by gel filtration to be ∼200 kilodaltons. These properties of Leu-Phe-cleaving activity indicate that the Leu-Phe-cleaving enzyme is distinct from any known brain endopeptidase.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1471-4159.1989.tb07249.x
