Hydrolysis of Amino‐acid Esters by Alkaline Mesentericopeptidase

The V max and K m values for the hydrolysis of Nα‐tosyl‐L‐arginine methyl ester, Nα‐benzoyl‐L‐arginine methyl ester, N‐acetyl‐L‐tryosine ethyl ester and N‐benzoyl‐L‐tyrosine ethyl ester by alkaline mesentericopeptidase were determined. It is concluded that there is a similarity in the esterolytic properties of mesentericopeptidase and the subtilisins. Mesentericopeptidase is nearer to subtilisins Novo and Amylosacchariticus than to subtilisin Carlsberg. The K m values for the hydrolysis of Na‐tosyl‐L‐arginine methyl ester by alkaline mesentericopeptidase were approximately constant over the pH range 5.5 to 8.0. A pK of 6.6 at 37° C was determined from the sigmoid pH‐velocity profile for the hydrolysis of this substrate. The data indicate that there is an imidazole group in the active site of the alkaline protease from Bac. mesentericus that must be non‐protonated for hydrolysis to take place. The amino acid compositions of mesentericopeptidase and subtilisin Amylosacchariticus are almost identical, but there are differences in the mechanism of action of these two enzymes. The conclusion is drawn that alkaline mesentericopeptidase belongs to the subtilisin BPN'‐group of alkaline proteases according to the classification of Keay & Moser ( 14 ).