Sensitization of D-glucuronic acid transport system of E. coli to protein group reagents in presence of substrate or absence of energy source

N-ethylmaleimide and 1-fluoro-2,4-dinitrobenzene inactivate D-glucuronic acid transport in $\text{E. coli}$ K12. The inactivation is highly enhanced by the two substrates of the transport system, D-glucuronate and D-galacturonate, or by inhibitors of respiratory energy production. The significance of these results is discussed in the framework of a model of a mobile carrier which can exist in two or more distinct conformational states.