Summary: Ureases of the cyanobacteria PCC 73110 and PCC 7120 were purified more than 1500-fold to homogeneity by heat treatment and liquid chromatography, reaching specific activities of up to 350 U (mg protein). Both enzymes had a molecular mass of 220 kDa, as shown by native PAGE, and consisted of three subunits (α, β, γ) with molecular masses of 66 kDa (α), 18 kDa ( or 14 kDa (AnabaenalNostoc; β) and 11 kDa (γ). The enzyme of exhibited maximum activity at pH 8.2 and 60 °C, and that of nabaenalNostoc at pH 8.5 and 65 °C; the was 0.25 mM urea for both organisms. Almost identical specific activities were observed in cells grown with urea, ammonia, nitrate or dinitrogen as the source of nitrogen. The ureases from both organisms were heat-stable; no loss of activity was observed during incubation at 70 °C for 15 min.


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