Thermolysin is a well‐known protease which exhibits its specificity against hydrophobic amino acid residues such as l‐leucine, l‐phenylalanine, etc. whose amino groups donate the susceptible peptide bonds (amino‐endopeptidase). The present study was undertaken to investigate the effects of neighboring residues surrounding the sensitive amino acid residues at the amino‐side in peptide substrates. For the purpose, a kinetic study was made using various synthetic oligopeptides such as Z‐A‐(Gly)n↑–Leu‐Ala or Z‐Gly–↑Leu‐(Gly)n‐B (A or B = various d‐ or l‐amino acid residues; n= 0, 1 and/or 2; the arrow shows the bond split) as substrates. Other kinetic or inhibition studies were also made. These studies indicated that the specificity is affected by at least three amino acid residues on the N‐terminal side and by two amino acid residues on C‐terminal side from the sensitive amino acid residue (at amino‐side) in peptide substrates. The effect of each of the five neighboring amino acid residues for appearance of the specificity was similar with that of the corresponding one which had been observed in a neutral protease of Bacillus subtilis, but that was not completely the same.
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