Formation of desTyr dynorphins 5-17 by a purified cytosolic aminopeptidase of rat brain

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Abstract
An aminopeptidase purified to homogeneity from cytosol of rat brain cleaved dynorphins having 5–17 residues and selected proenkephalins at the Tyr–Gly bond only to release Tyr and the desTyr fragments. The enzyme protein consisted of a single polypeptide chain of Mr 103,000 and was inhibited by puromycin, bestatin, and chelating reagents to yield Ki in the micromolar range. Hydrolysis of Leu-2-naphthylamide was inhibited by Dyn 1–5 competitively (Ki, 18 μM); the Km for Dyn 1–5, the best substrate of the series, was 63.8 μM (Kcat/Km ratio 580 mM−1 min−1). Rates of N-tyrosyl release decreased with peptide size; the presence of Arg in position 6 led to 50% loss for Dyn 1–6, and the C-terminal extensions of Dyn 1-13 or 1–17 to a 98% loss in activity as compared to the pentapeptide. Rapid degradation of small peptides is consistent with a paracrine (neurotransmitter) role as compared to the postulated precursor or exocrine roles for the dynorphins with 13 residues or more.