SUMMARY: The cyanobacterium Anabaena cylindrica was found to have nickel-dependent urease activity. Addition of nickel to a nickel-free culture led to recovery of urease activity. This was not prevented by chloramphenicol. Cell-free extracts of nickel-depleted cells did not regain activity upon addition of Ni2+. Enzyme synthesis was constitutive; similar urease activities occurred in urea-, NO−3- or NH3-grown cultures or those grown under N2-fixing conditions. The urease activity had hyperbolic kinetics, with an apparent Km with respect to urea of 1.3 ± 0.6 (SD) mM. Enzyme activity was enhanced up to two fold by MgSO4 and MnSO4 at pH 7.5. At 10 mM-urea, cells hydrolysed urea and excreted NH3 in excess of biosynthetic requirements.
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