Current address: Geosciences Department, Guyot Hall, Princeton University, Princeton, NJ 08544.
ASSAY OPTIMIZATION AND REGULATION OF UREASE ACTIVITY IN TWO MARINE DIATOMS
Version of Record online: 25 DEC 2001
Journal of Phycology
Volume 36, Issue 3, pages 523–528, June 2000
How to Cite
Peers, G. S., Milligan, A. J. and Harrison, P. J. (2000), ASSAY OPTIMIZATION AND REGULATION OF UREASE ACTIVITY IN TWO MARINE DIATOMS. Journal of Phycology, 36: 523–528. doi: 10.1046/j.1529-8817.2000.99037.x
- Issue online: 23 JUL 2003
- Version of Record online: 25 DEC 2001
- 1 Received 11 March 1999. Accepted 25 January 2000.
- nitrogen assimilation;
- organic nitrogen;
- Thalassiosira spp;
- urease assay
An in vitro urease enzyme assay was developed for the marine diatoms Thalassiosira pseudonana Hasle et Heimdal (clone 3H) and T. weissflogii (Grunow) Fryxell et Hasle (clone Actin). This assay involves the colorimetric measurement of ammonium following the hydrolysis of urea in crude cell homogenates and it is the first assay to account for the rate of nitrogen assimilation in both species grown on urea as the sole nitrogen source. Urease activity was found to be present regardless of nitrogen source, although activities showed distinctly different patterns depending on the species examined and form of nitrogen supplied. Under nitrogen-replete conditions, urease activity in T. pseudonana was present constitutively when grown on NH4+ and upregulated when grown on NO3− or urea. In nitrogen-replete T. weissflogii, urease activity was present at high constitutive levels regardless of the nitrogen source and showed no upregulation. Nitrogen starvation did not upregulate activity in either species.