Acylation of the alanine149 N-terminal of alpha-chymotrypsin and its effect on catalytic function.

A novel, active derivative of alpha-chymotrypsin was prepared from alanine-neochymotrypsinogen in which the epsilon-amino groups and the alpha-amino group of N-terminal Ala149 were acetylated. The catalytic properties at neutral and alkaline pH of this enzyme derivative were compared with those of a control alpha-chymotrypsin derivative in which only the epsilon-amino groups were acetylated. While the Km (app) of the two derivatives were the same at pH 7 to 8, at more alkaline pH the derivative having the masked Ala149 had much lower Km (app) values than the control. It is concluded that the inactivation of alpha-chymotrypsin at high pH is linked, at least in part, to the ionization state of its N-terminal Ala149 group.