HEAT-STABLE UREASES FROM 2 FILAMENTOUS CYANOBACTERIA

Ureases of the cyanobacteria Leptolyngbya boryana (Plectonema boryanum) PCC 73110 and Anabaena/Nostoc 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)-1. Both enzymes had a molecular mass of 220 kDa, as shown by native PAGE, and consisted of three subunits (alpha, beta, gamma) with molecular masses of 66 kDa (alpha), 18 kDa (Leptolyngbya; beta) or 14 kDa (Anabaena/Nostoc; beta) and 11 kDa (gamma). The enzyme of Leptolyngbya exhibited maximum activity at ph 8.2 and 60 degrees C, and that of Anabaena/Nostoc at ph 8.5 and 65 degrees C; the K-m 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 degrees C for 15 min.