Studies on the chemical modification of trypsin.

Many effects of dibenamine (Â /V-dibenzyl-/?chloroethylamine) on physiological systems have been reviewed by Graham1 and Nickerson2. However their effect on enzyme activity was not reported till Beddoe and Smith 3 observed that dibenamine also reacts with acetylcholinesterase under rather specific conditions in an irreversible manner to give an in­ active modified enzyme. The inhibiting compound for the reaction is probably the ethyleniminium ion which is present in high concentration in solu­ tions of dibenamine hydrochloride which are nor­ mally acid (pH 3.2). Reaction between alkylating compounds and the enzyme does not occur in the acid solution but occurs in near neutral media where a functional group on the enzyme is in the correct state of ionization. The alkylating compound is very unstable at near neutral pH and decomposes within a minute or so. Consequently inhibition is only ob­ served when either the dibenamine solution is added to the enzyme at near neutral pH or an acidic mixture of the two is rapidly raised to near neutral pH. The present study was undertaken to determine the effects of inhibition on the structure of trypsin.