Semax and Selank inhibit the enkephalin-degrading enzymes of human serum

Dose-dependent effect of synthetic heptapeptides Semax (Met-Glu-His-Phe-Pro -Gly-Pro) and Selank (Thr-Lys-Pro-Arg-Pro-Gly-Pro) on the enkephalin-degrad ing enzymes of human serum was demonstrated. The inhibitory effects of Sema x (IC50 10 muM) and Selank (IC50 20 muM) are more pronounced than that of p uromycin (IC50 10 mM), bacitracin, and some other inhibitors of peptidases. Beside the heptapeptides, their pentapeptide fragments also possessed an i nhibitory effect; tri-, tetra- and hexapeptide fragments did not display su ch an effect. As the above enzymes take part in degradation of not only enk ephalins but also other regulatory peptides, it can be assumed that one of the mechanisms of biological activity of Semax and Selank is related to thi s inhibitory activity of theirs.