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Ammonium Assimilation by the Nitrateutilizing Yeast, Candida nitratophila

C. R. Hipkin, K. J. Flynn, E. Marjot, Z. S. Hamoudi and A. C. Cannons
The New Phytologist
Vol. 114, No. 3 (Mar., 1990), pp. 429-434
Published by: Wiley on behalf of the New Phytologist Trust
Stable URL: http://www.jstor.org/stable/2557189
Page Count: 6
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Ammonium Assimilation by the Nitrateutilizing Yeast, Candida nitratophila
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Abstract

Ammonium-nitrogen was assimilated rapidly by nitrogen-replete cultures of the nitrate-utilizing yeast, Candida nitratophila as long as a suitable source of carbon was available. These cultures contained high activities of an NADPH-dependent glutamate dehydrogenase with a relatively high affinity for ammonium (Km = 0.27 mM) and high glutamine synthetase activity. Both enzyme activities were apparently derepressed when glutamine-grown cultures were starved of nitrogen or transferred to nitrate medium. Nitrogen-deficient cultures also contained NADH-dependent glutamate synthase activity that was inhibited by azaserine in vitro. Ammonium assimilation in vivo, was inhibited by methionine sulphoximine whilst addition of azaserine resulted in an accumulation of intracellular glutamine and an inhibition of glutamate production. Our results suggest that, in C. nitratophila, there is a potential for ammonium assimilation via both the glutamate dehydrogenase pathway and the glutamine synthetase/glutamate synthase pathway with the latter pathway predominating in nitrogen-deficient cells.

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