Identification of a proenkephalin precursor in striatal tissue

Area of Science:

• Neuroscience
• Biochemistry
• Molecular Biology

Background:

• Proenkephalin is processed into enkephalins in both the adrenal medulla and brain.
• Enkephalin intermediates from proenkephalin have been identified in the adrenal medulla but not the brain.
• The absence of brain intermediates suggested extremely rapid proenkephalin processing.

Purpose of the Study:

• To investigate the presence and characteristics of enkephalin-containing intermediates in the brain.
• To determine if proenkephalin processing in the brain involves detectable intermediate forms.

Main Methods:

• Sephacryl-300 gel filtration chromatography of guinea pig, rat, and bovine striata.
• Enzymatic digestion with trypsin followed by carboxypeptidase B.
• Chromatofocusing, SDS-PAGE, nitrocellulose blotting, and radioimmunoassays.

Main Results:

• Several peaks of bioactive and immunoreactive enkephalin-like peptides were detected in striatal extracts.
• A major species with an apparent molecular weight of 29,000 was identified in guinea pig striata.
• This major species, characterized further, contained (Met5)-enkephalin, (Leu5)-enkephalin, and (Met5)-enkephalin-Arg6-Phe7 in a 6:1:1 ratio.

Conclusions:

• Enkephalin-containing intermediates derived from proenkephalin are present in the brain.
• These intermediates accumulate and can be isolated, contrary to previous assumptions.
• The findings suggest a more complex processing pathway for proenkephalin in the brain than previously thought.