The electrochemical proton gradient and phenylalanine transport in Escherichia coli irradiated with near-ultraviolet light.

Irradiation of Escherichia coli with near-ultraviolet (near-UV) light diminished the electrochemical proton gradient and the accumulation of L-phenylalanine. Inhibitors known to collapse the proton gradient and the comparison of two techniques measuring the electrical potential substantiated the estimates made. At several fluences (doses), a linear relationship was observed between the phenylalanine gradient and the combined electrical and chemical potentials (the electrochemical proton gradient), suggesting a close coupling between them. However, additional effects of near-UV light on the phenylalanine permease were not discounted. The combined potentials provided sufficient energy for the observed accumulation of phenylalanine, assuming a proton to amino acid cotransport ratio of 1. An increase in membrane permeability did not contribute to the loss of phenylalanine transport, as shown by an increase in the rate and extent of alpha-methylglucoside uptake.