Urea metabolism and urease regulation in the cyanobacterium Anabaena variabilis

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Abstract
Anabaena variabilis can use urea as a nitrogen source, which it breaks down via the action of urease. No evidence of urea amidolyase activity was found. Urease synthesis is constitutive; no major difference in enzyme levels was found when cultures were grown with urea, ammonia, or N2. Urea is not required for urease synthesis, and ammonia does not repress urease synthesis. However, urea does repress nitrogenase synthesis at the transcription level, probably by the same mechanism as ammonia. Anabaena variabilis urease is inhibited by phenylphosphorodiamidate, hydroxyurea, and acetohydroxamic acid, which suggests that the enzyme contains nickel. A Km for urea of 46 μM was observed in crude cell free extracts. The enzyme is cytoplasmic and relatively heat resistant. Key words: urea, urease, cyanobacteria, Anabaena variabilis.

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