Structure and function of symporter and antiporter

Structure and function of symporters and antiporters which utilize Na+ as the coupling cation are briefly reviewed. The SGLT is an Na+/glucose symporter present in animal cell membranes. So far, five isoforms of the SGLT (1 to 5) have been found in various tissues. The Me1B is an Na+/galactoside symporter present in membranes of enteric bacteria. Regions or amino acid residues of these symporters which are important for substrate recognition or cation recognition have been identified. Furthermore amino acid substitutions in the SGLT1 of glucose-galactose malabsortion families have been identified. Regions and amino acid residues which are important for the function of the Na+/H+ antiporters (or exchangers) which extrude H+ (in animal cells) or Na+ (in bacterial cells) have been also identified.