JACK BEAN UREASE - MIXED-METAL DERIVATIVES

We have prepared, for the first time, mixed-metal (Zn/Ni and Co/Ni) de rivatives of the nickeloenzyme, urease. The mixed-metal derivatives, a lthough possibly catalytically inert, provide a means for the further investigation of both the catalytic mechanism and coordination of the native nickel ions. A study of the specific activity of nickel-deplete d urease indicates that the loss of one nickel ion is sufficient to re nder it inactive. Sulfite was found to play a key role in stabilising the urease-bound nickel. The visible spectrum of the pink Co/Ni urease is presented. Together, these results provide additional evidence for a difference in the ligation of the jack bean urease active-site nick el ions and comment on the possibility of a variety of ligation geomet ries. Examination of the sequences of the enzymes from Klebsiella aero genes and the jack bean reveals that there is an exact match, residue for residue, between the critical ligating and active-site residues of the Klebsiella enzyme (alpha-chain residues: Asp 360, Cys 319, His 27 2, His 246, His 136, His 134 and carboxylated Lys 217) and those of th e jack bean enzyme (Asp 633, Cys 592, His 545, His 519, His 409, His 4 07 and Lys 490), and this lends strong support to essentially identica l mechanisms of action for the two enzymes.