Low molecular weight peptide inhibitors of medullasin: purification and structure

Two low molecular weight peptide inhibitors of medullasin were isolated from human bone marrow cells. Determination of their amino acid composition and amino acid sequence revealed that one inhibitor was composed of 36 amino acid residues and the other 34 amino acid residues which are identical with the C-terminal portions (Formula; see text) of the beta-chain of human hemoglobin. These two peptides when synthesized also showed the same degree of inhibitory effect on medullasin activity as the natural products. Neither the N-terminal portion of the inhibitor, composed of 21 amino residues, nor the C-terminal peptide, composed of 20 amino acids, inhibited medullasin activity. Medullasin was inhibited reversibly and non-competitively against by these inhibitors and was the most effectively inhibited serine protease among several tested.