The periplasmic galactose receptor protein of Escherichia coli in relation to galactose chemotaxis.

The periplasmic galactose receptor protein of E. coli is the common macromolecule in the initiation of two functions, chemotaxis and active transport. The substrates are glucose and galactose and the affinity for binding to the receptor protein is high (Kp -2 X 10(-8) M for glucose and 1 X 10(-7) M for galactose). A second binding site shows a 100-fold lower affinity. The high concentration of the galactose receptor protein in the periplasmic space tends to give retention through recapture of the ligands. The kinetic properties of the galactose receptor protein are, in general, in harmomy with the kinetics of chemotactic responses to spatial or temporal sugar gradients.