INACTIVATION OF THE LACTOSE PERMEASE OF ESCHERICHIA-COLI BY MONOCHROMATIC ULTRAVIOLET-LIGHT

Abstract— The lactose permease of E. coli is inactivated exponentially by seven wavelengths of monochromatic UV light. An action spectrum reveals that the shorter wavelengths (243, 290 and 313 nm) are much more efficient than longer wavelengths. Inactivation at 290 nm is most efficient and is not due to generalized membrane damage. The rate of counterflux of intracellular β‐galactoside in response to externally added β‐galactoside was slowed by 290 nm irradiation, indicating destruction of the facilitated diffusion mechanism. The induction of β‐galactosidase and β‐galactoside permease was co‐ordinate both with and without pre‐irradiation by 290 nm light. The β‐galactosidase is approximately 26‐fold more resistant to 290 nm than the permease. These results are discussed in terms of a greater sensitivity of membrane proteins to 290 nm light, which may be due to the role of aromatic amino acids in conferring stability to the permease in the membrane. Copyright © 1979, Wiley Blackwell. All rights reserved