Jack bean urease (EC 3.5.1.5). II. The relationship between nickel, enzymatic activity, and the "abnormal" ultraviolet spectrum. The nickel content of jack beans

Abstract

At low pH, EDTA promotes the loss of the tightly bound Ni ions from jack bean urease. The specific activity of soluble enzyme after partial EDTA-promoted inactivation is a linear function of the Ni content. The results are consistent with the presence of 2.0 Ni ions per 97,000 dalton subunit in pure urease. The time scale for loss of enzymatic activity and Ni under these conditions is similar to that for loss of the abnormal tail absorption in the UV and visible absorption spectrum of urease (including the shoulder at .apprx. 420 nm). This indicates that Ni in urease is essential for enzymatic activity and establishes that the metal ions are in part responsible for the tail absorption in the UV spectrum of urease. After partial inactivation in the presence of EDTA either at low pH or in 2.5 M guanidinium chloride at neutral pH, urease did not regain activity in the presence of Ni2+. As yet apourease has not been produced reversibly. Jack bean seeds grown hydroponically without added Ni were low in both urease activity and Ni (10 and 6%, respectively, of parent seeds). Several other metal ions were readily available. Apparently, metal ions other than Ni cannot substitute for Ni in the formation of normally active urease.