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Title: Studies on urea metabolism in some unicellular algae
Author: Leftley, J. W.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1980
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1. 16 strains of unicellular algae, representing 3 phyla and 6 classes, were assayed for the presence of the enzymes urease and ATP: urea amidolyase (UALase) when grown on urea as the sole source of nitrogen. All the algae examined that are unequivocally classed as Chlorophyceae contained UALase, but not urease. All the other algae examined contained urease, but not UALase. The relevance of these findings to the phylogeny of algae is discussed. 2. Urease from Phaeodactylum tricornutum (Bacillariophyceae) was purified three-fold and found to have an apparent Km of 0.5 mM. UALase from Dunaliella primolecta (Chlorophyceae) was purified five-fold, and the apparent Km was approximately 0.1 mM. The urease in Phaeodactylum appeared to be constitutive, since the enzyme activitities measured in algae grown on ammonium, nitrate, nitrite, arginine or uric acid as sole source of nitrogen were similar to those in algae grown on urea. In contrast, UALase in Dunaliella was inducible in that it could only be detected in cells grown on urea. 3. The half-saturation constant (Ks) for the decomposition of urea by whole cells of Phaeodactylum and Dunaliella was determined and, in both cases, was found to be in the order of 1.5 UM. Problems associated with the method are discussed. 4. The accumulation of urea by Phaeodactylum and Dunaliella was measured. It was calculated that P. tricornutum could accumulate 4 mnol of urea per dm3 of packed-cell volume, which would be sufficient to saturate the urease in this alga. No urea accumulation could be detected in Dunaliella. The relationship between Km and Ks is discussed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available