A Study of the Structural Subunits of Urease Obtained During Controlled Dissociation

Abstract

Native urease, an enzyme with a preparative molecular weight of 480 000, has been dissociated stepwise to 60 000 and 30 000 molecular weight subunits. The 60 000 dalton species was obtained by exposure to 9 M urea. It is enzymatically active, with a specific activity approximately 45% of the native enzyme, and possesses a substantially less ordered structure. A presumptive dissociation to 90 000 dalton species was obtained by exposure to 8 M urea. This dissociation proceeds with conservation of approximately 90% of the enzymic activity of native urease and conservation of the ordered structure. Both 60 000 and 90 000 dalton species were also obtained by exposure of urease to 3 M or 6 M guanidine hydrochloride. These preparations were heterogeneous, enzymatically inactive, and suffered severe structural loss. Dissociation to a 30 000 dalton structural subunit was observed after treatment of urease with acetate–acetic acid at pH 2.2. The dissociation appeared to be a symmetrical process leading to physically identical subunits and conserving the ordered structure of the enzyme. Under the normal assay conditions the 30 000 dalton species polymerizes and this prevents conclusive proof of enzymic activity at this time.