Brain endopeptidase generates enkephalin from striatal precursors

Area of Science:

• Neuroscience
• Biochemistry
• Enzymology

Background:

• Opioid peptides, such as enkephalins, play crucial roles in pain modulation and reward pathways.
• The biosynthesis of enkephalins involves the processing of larger precursor peptides.
• Enzymatic mechanisms for generating free enkephalin from its precursors are not fully elucidated.

Purpose of the Study:

• To purify and characterize an enzyme responsible for converting opioid peptide intermediates to free enkephalin.
• To compare the activity of this enzyme with known processing enzymes like carboxypeptidase B.
• To investigate the role of this enzyme in the post-translational processing of enkephalin precursors in the rat brain.

Main Methods:

• Purification of enkephalin-generating endopeptidase (EGE) from rat brain membranes.
• Comparative enzymatic assays using trypsin and EGE versus trypsin and carboxypeptidase B on rat striatal precursor peptides.
• Sephadex G-100 gel filtration and radioimmunoassay for enkephalin quantification.
• High-performance liquid chromatography (HPLC) analysis of enzymatic reaction products.

Main Results:

• A 300-fold purification of EGE was achieved from rat brain membranes.
• EGE demonstrated the ability to convert opioid peptide intermediates into free enkephalin.
• EGE activity, when combined with trypsin, produced enkephalin levels comparable to those generated by trypsin and carboxypeptidase B.
• HPLC analysis confirmed that EGE treatment increased enkephalin and Leu-enkephalin levels.

Conclusions:

• EGE is a key enzyme in the brain capable of processing proenkephalin precursors into bioactive enkephalins.
• EGE functions effectively after the action of trypsin-like enzymes in the brain.
• The enzyme's activity is inhibited by specific small peptides, suggesting substrate specificity.