Isolation and identification of an endogenous inhibitor of enkephalin-degrading enzymes from bovine spinal cord.

We isolated a potent inhibitor of enkephalin-degrading enzymes from bovine spinal cord and determined its amino-acid sequence and inhibitory activity toward enkephalin-degrading enzymes. This new substance, designated spinorphin, is composed of a heptapeptide (Leu-Val-Val-Tyr-Pro-Trp-Thr). The inhibitory activity (IC50) of this new substance toward enkephalin-degrading enzymes, purified from monkey brain, was found to be 3.3 micrograms/ml against aminopeptidase, 1.4 micrograms/ml against dipeptidyl aminopeptidase, 2.4 micrograms/ml against angiotensin-converting enzyme, and 10 micrograms/ml against enkephalinase. This new substance did not show inhibitory activity toward enkephalin degrading enzymes purified from kidney and blood. Above results suggest that this substance is a new neuromodulator in the spinal cord.