Preparation and kinetic properties of a new form of chymotrypsin which is active at alkaline pH: 1 -chymotrypsin.

The preparation of a new stable and active form of chymotrypsin is described. The enzyme possesses threonine-147 instead of alanineas the NH&erminal group of the C chain and has been called ai-chymotrypsin. The conformational transition that affects chymotrypsins at alkaline pH was investigated and compared with that of 01and &chymotrypsins by studying the kinetic constants and their pH dependencies for the hydrolysis of various specific ester substrates. The keal values obtained with LYEchymotrypsin are similar to those of o(and 6-chymotrypsins. The K, values showed a progressive increase toward the alkaline pH region. The shape of the K,-pH profiles closely resemble those of &chym.otrypsin and differ considerably from the behavior of cr-chymotrypsin. The results strongly implicate the participation of the alanineamino group in the reversible inactivation of oc-chymotrypsin at high pH.