SODIUM-STIMULATED TRANSPORT OF GLUTAMATE BY THERMUS-THERMOPHILUS STRAIN-B

Thermus thermophilus B is one of the many Thermus strains able to util ize glutamate as a sole source of carbon. Sodium is an obligate requir ement for glutamate transport by washed whole cells, but the affinity for sodium (K(m) = 23 mM) is low. At pH 7.6, uptake of glutamate is ra pid in 50 mm-sodium at 65-degrees-C and obeys saturation kinetics with an apparent K(m) of 0.23 muM-glutamate and a V(max) of 12 nmol glutam ate min-1 (mg protein)-1. The transport system is insensitive to osmot ic shock and is specific for glutamate, with both the L- and D-isomers being transported. Uptake is very sensitive to inhibitors that collap se the membrane potential (DELTApsi) or the chemical gradient of sodiu m ions (DELTApNa), but a transmembrane pH gradient (DELTApH) plays no role in the transport of glutamate. These results are therefore consis tent with a membrane sodium/glutamate symport system.