Sodium-substrate cotransport in bacteria

A variety of sodium-substrate cotransport systems are known in bacteria. So dium enters the cell down an electrochemical concentration gradient. There is obligatory coupling between the entry of the ion and the entry of substr ate with a stoichiometry (in the cases studied) of 1:1. Thus, the downhill movement of sodium ion into the cell leads to the accumulation of substrate within the cell. The melibiose carrier of Escherichia coli is perhaps the most carefully studied of the sodium cotransport systems in bacteria. This carrier is of special interest because it can also use protons or lithium i ons for cotransport. Other sodium cotransport carriers that have been studi ed recently are for proline, glutamate, serine-threonine, citrate: and bran ched chain amino acids. (C) 2001 Elsevier Science B.V. All rights reserved.