TRKH AND ITS HOMOLOG, TRKG, DETERMINE THE SPECIFICITY AND KINETICS OF CATION-TRANSPORT BY THE TRK SYSTEM OF ESCHERICHIA-COLI

The corrected sequence of the trkH gene of Escherichia coli predicts that the TrkH protein is a hydrophobic membrane protein of 483 amino acid residues, of which 41% are identical to those of the homologous and functionally analogous TrkG protein. These two proteins form the transmembrane component of the Trk system for the uptake of K+. Each protein alone is sufficient for high-level Trk activity. When Trk is assembled with the TrkG protein, Rb+ and K+ are transported with a K-m near or below 1 mM; however, the V-max for Rb+ is only about 7% of that for K+. When Trk is formed with TrkH, the affinities for both for K+ and Rb+ are somewhat lower, and the V-max for Rb+ is only 1% of that for K+ transport. The kinetics of transport in strains with wild-type alleles at trkG and at trkH suggest that both products participate in transport.