Introduction

Urease catalyzes the hydrolysis of urea into ammonia and CO2. This enzyme enables the utilization of other nitrogenous compounds, such as ureides, whose N can be used exclusively as urea. Moderate levels of urease activity (ca. 300 nmol min.mg protein"1) were detected in Rhizobium leguminosarum bv. viciae UPM791 vegetative cells. This activity did not require urea for induction, and was partially repressed by the addition of ammonium. Also, this bacterium was able to use other urea-rendering compounds (inosine, hypoxanthine, xanthine, urate) as nitrogen source. This ability was dependent on the presence of urease activity. A role for urease in internal urea metabolism rather than in use of external urea is inferred because urease deficiency led to the excretion of urea when cells were grown with arginine as N source. Lower urease activities (ca. 100 nmol min.mg protein"1) were measured in bacteroids obtained from pea nodules. Urease-deficient derivatives of this strain were not impaired in either nitrogenase or hydrogenase in bacteroids.

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