Factors influencing the inactivation of urease by alkylating agents.

In the production of biological effects such as vesication by bis-p-chloroethyl sulfide (mustard gas) it has been considered probable that inactivation of tissue enzymes is of foremost importance. In view of the reaction characteristics of bis-p-chloroethyl sulfide it has appeared likely that this inhibition is due to an alkylation reaction involving essential groups of the enzymes. Involvement of sulfhydryl groups especially has been suggested by knowledge of the high reactivity of bis-p-chloroethyl sulfide with such groups in simple compounds. To furnish information on some of the factors affecting this mechanism of enzyme inhibition, an investigation and comparison have been made of the influence of hydrogen ion, phosphate, and alkylating agent concentrations, and the state of activity on the inactivation of a single enzyme, urease, by bis$?-chloroethyl sulfide and by several other agents of somewhat differing characteristics. This particular enzyme was chosen, not because of any supposed involvement of urease in vesication, but because many of the physical and chemical properties of urease have already been characterized and its ureolytic activity, which is conveniently measurable, has been well demonstrated to depend upon the freedom of specialized sulfhydryl groups (1). The alkylating agents considered in this study were bis-p-chloroethyl sulfide, its half hydrolysis product, P-chloro-P’-hydroxydiethyl sulfide (also known as semi-H), and an oxidation product, divinyl sulfone. For comparative purposes inactivation by benzoquinone, 2-methyl-1,4-naphthoquinone, and iodine was also investigated. It was to be expected that differences would be found in the behavior of the chloroethyl sulfides and divinyl sulfone, for although they are all vesicant alkylating agents reacting readily with sulfhydryl groups, they have different reactivities with respect to other groups. There is a distinct contrast in the stabilities of these compounds in water; the chloroethyl sulfides hydrolyze readily with the production of innocuous thiodiglycol and hydrochloric acid, while divinyl sulfone