UREA UPTAKE AND UREASE ACTIVITY IN CORYNEBACTERIUM-GLUTAMICUM

When Corynebacterium glutamicum is grown with a sufficient nitrogen su pply, urea crosses the cytoplasmic membrane by passive diffusion. A pe rmeability coefficient for urea diffusion of 9 x 10(-7) cm s(-1) was d etermined. Under conditions of nitrogen starvation, an energy-dependen t urea uptake system was synthesized. Carrier-mediated urea transport was catalyzed by a secondary transport system linked with proton motiv e force. With a K-m for urea of 9 mu M, the affinity of this uptake sy stem was much higher than the affinity of urease towards its substrate (K-m approximately 55 mM urea). The maximum uptake velocity depended on the expression level and was relatively low [2-3.5 nmol min(-1) (mg dry wt.)(-1)].