GLUTAMINE UPTAKE BY A SODIUM-DEPENDENT SECONDARY TRANSPORT-SYSTEM IN CORYNEBACTERIUM-GLUTAMICUM

Corynebacterium glutamicum took up glutamine by a sodium-dependent sec ondary transport system. Both the membrane potential and the sodium gr adient were driving forces. Glutamine uptake showed Michaelis-Menten k inetics, with a K-m of 36 mu M and a V-max of 12.5 nmol min(-1) (mg dr y weight)(-1) at pH 7. Despite a pH optimum in the alkaline range arou nd pH 9, it was shown that uncharged glutamine is the transported spec ies. The affinity for the cotransported sodium was relatively low; an apparent K-m of 1.4 mM was determined. Among various substrates tested , only asparagine, when added in 50-fold excess, led to an inhibition of glutamine transport. It was concluded that glutamine uptake occurs via a specific transport system in symport with at least one sodium io n.