Nickel-content of urease from Bacillus pasteurii

Urease from Bacillus pasteurii DSM 33 was purified 34-fold to a maximum specific activity of 996.5 mumol urea min-1 mg-1 at 30 degrees C. Homogeneity was demonstrated by isoelectric focussing which showed a single protein zone corresponding to a pI of about 4.6. The native enzyme was demonstrated to have a molecular mass of 230,000 and to consist of identical subunits of 65,500, as measured by SDS electrophoresis. Radioactive 63Ni-nickel co-chromatographed with urease through gel filtration, ion-exchange, and affinity chromatography. Measuring specific radioactivity, the nickel content was found to be 1.00 (+/- 0.1) g-atom Ni per mol of subunit, and 0.82 g-atom Ni per mol as measured by atomic absorption spectrometry. This indicates that 1 atom of nickel is present in each of four subunits of the enzyme.