Figure 4.

Demethylation of Tar and TarΔpp catalyzed by CheB and phospho-CheB. (A) Action of CheB on receptors alone. Membranes providing ≈10 μM Tar or TarΔpp modified with ³H-methyl groups as described for Fig. 3 (≈0.4 methyls per receptor) were mixed with 0.5 μM purified CheB. Samples containing ≈40 pmol receptor were removed at the indicated times and analyzed for released ³H-methanol. (B) Action of CheB and phospho-CheB on receptors alone. Receptor-containing membranes as in A were incubated 15 min with 5 μM CheA, 1 mM ATP was added to some incubations (plots labeled CheB-P), the incubation continued for 15 min, purified CheB was added to 0.5 μM, and samples were taken and analyzed as for A. (C) Action of CheB and phospho-CheB on receptors complexed with CheA and CheW. Receptor-containing membranes as in A were incubated 30 min with 5 μM CheA and 5 μM CheW. CheB or CheB plus ATP (plots labeled CheB-P) were added to 0.5 μM CheB and 1 mM ATP, and samples were taken and analyzed as for A. For all panels, data are averages of experiments on at least three separate membrane preparations. Error bars show SEs.