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N-terminal of Leu-norleucinal or Leu-methioninal was modified to obtain a cell penetrative peptide inhibitor against calpain. Benzyloxycarbonyl (Z) derivatives had less active against papain than phenylbutyryl derivatives and leupeptin. Z-Leu-nLeu-H (calpeptin) was more sensitive to calpain I than Z-Leu-Met-H and leupeptin. Calpeptin was most potent among synthesized inhibitors in terms of preventing the Ca2+-ionophore induced degradation of actin binding protein and P235 in intact platelets. After 30 min incubation with intact platelets, calpeptin completely abolished calpain activity in platelets but no effect was observed in case of leupeptin. Calpeptin also inhibited 20K phosphorylation in platelets stimulated by thrombin, ionomycin or collagen. Thus calpeptin was found to be a useful cell-penetrative calpain inhibitor.

Analogs of the mating factor of Saccharomyces cerevisiae, Trp1- Trp3-Leu-Gln-Leu6-Lys7-Pro8-Gly-Gln-Pro11-Met12-Tyr13, from which amino acids were eliminated or substituted for other amino acid, were synthesized. These analogs showed lower biological activity than the natural mating factor if assayed after 6 hours incubation with a-mating type cells of S. cerevisiae. However, if assayed after 24 or 48 hours incubation, the situation changed, i.e. the analogs in which Leu6 or Lys7 were replaced by the corresponding D-isomer, showed higher mating factor activity than the unsubstituted mating factor. The same result was obtained with the analogs in which Met was replaced by norleucine.

The mating factor of Saccharomyces cerevisiae, Trp-His-Trp-Leu-Gln-Leu-Lys-Pro-Gly-Gln-Pro-Met-Tyr, has been synthesized to confirm the structure of the natural mating factor. The tridecapeptide has the same biological activity as the natural mating factor. From the studies on the biological activity of its truncated peptide synthesized the minimum sequence of the peptide require for the mating factor was deduced to be as His-Trp-Leu-Gln-Leu-Lys-Pro-Gly-Gln.