Formation of [Leu5]Enkephalin from Dynorphin A(1–8) by Rat Central Nervous Tissue In Vitro

3H]Dynorphin A(1-8) is readily metabolised by rat lumbosacral spinal cord tissue in vitro, affording a variety of products including a significant amount (20% recovered activity) of 3H]Leu5]enkephalin. In the presence of the peptidase inhibitors bestatin, captopril, thiorphan, and leucyl-leucine, 3H]Leu5]enkephalin was the major metabolic product, accounting for 60% of recovered activity. Production of 3H]Leu5]enkephalin was seen across all gross brain regions. The enzyme responsible for the cleavage has an optimal substrate length of 8-13 amino acids and is inhibited by N-1-(RS)-carboxy-2-phenylethyl]-Ala-Ala-Phe-p-aminobenzoate, a site-directed inhibitor of the metalloendopeptidase EC 3.4.24.15. However the enzymic breakdown also has properties in common with involvement of endo-oligopeptidase A. Possible consequences of the formation of Leu5]-enkephalin from the smaller dynorphins are discussed.