A relation between amino acid hydrophobicity and rate of uptake in Escherichia coli.

Fumarate and ferricyanide increased the rate of amino acid uptake in anoxic cells of E. coli suspended in a glycerol medium. The stimulation correlated with the hydrophobicity of 16 amino acids transported by several carrier systems. Fumarate and ferricyanide increased membrane energization as measured by changes in transmembrane pH and electrical potential, or by quenching of fluorescence of 1-anilino-8-naphthalenesulfonate. The results suggest that a common, rate determining step among the amino acid transport systems is the transfer of the substrate from an aqueous to an apolar environment.