(A) Effect of DCCD on [3H]-TPP binding by purified wild-type MdfA.
(B) Effect of substrates on the DCCD reactivity, as probed by inhibition of [3H]-TPP binding. The nonsubstrate nalidixic acid is shown as control.
(C) Effect of altering the proton concentration during reaction with DCCD on its reactivity, probed by inhibition of [3H]-TPP binding. The line represents a nonlinear regression fit to an equation of acid-base equilibrium-dependent modification.
(D and E) (D) MdfA(D34N) and (E) MdfA(E26Q): Effect of pH and TPP on DCCD reactivity.
(F) Single Cys mutant MdfA(D34C): Effect of substrates on mal-PEGylation (lower panel) and [3H]-TPP binding (upper panel). The nonsubstrate nalidixic acid was used as a control. All the experiments were repeated at least three times and the error bars represent SD. See also Figure S4. All modification reactions were carried at pH 6 unless indicated otherwise.