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Plant Physiology 50:642-644 (1972)
© 1972 American Society of Plant Biologists

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Effect of Urea on Ammonium-dependent Synthesis of Carbamyl Phosphate during Spore Germination of Geotrichum candidum

I. Barash, Ilana Lowy and S. Pomerantz

Department of Botany, Division of Mycology and Plant Pathology, Tel-Aviv University, Tel-Aviv, Israel

The specific activities of enzymes catalyzing the ammonium-dependent carbamyl phosphate synthesis (NH3-CPS) and the glutamine-dependent carbamyl phosphate synthesis (GLN-CPS) were increased during germination by approximately 5-and 1.7-fold respectively in the presence of 35 mM urea. The increase of NH3-CPS and GLN-CPS levels occurred immediately after the onset of germination and prior to the appearance of germ tube. Ammonium also stimulated the NH3-CPS activity, but the induction caused by urea was about three times higher than that by ammonium.

Both NH3-CPS and GLN-CPS were highly labile. NH3-CPS was obtained free of GLN-CPS after (NH4)2SO4 fractionation and diethylaminoethyl cellulose chromatography. The optimum pH for NH3-CPS was 8.5 as opposed to broad pH optimum of pH 5.6-8 for the reverse reaction. The Km values obtained for NH3, glutamine, and carbamyl phosphate were 12 mM, 0.5 mM, and 0.083 mM, respectively.






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Copyright © 1972 by the American Society of Plant Biologists