kfRr(L Second reduction LT p K ffA(l) t eff1(L) kef(L) pt eff3 2 LT LT 3 additional assumption CheB only demetylates phosphorylated receptors experimental backup not possible to directly measure if Cheb demethylate only active receptors rate of methylation drops immediately after addition of ligand indicates that CheB works on active receptorsT2 LT2 T3 LT3 T2p LT2p T3p LT3p keff1(L) keff2(L) keff3(L) keff4(L) keff3(L) kpt kpt Second reduction additional assumption: - CheB only demetylates phosphorylated receptors experimental backup: - not possible to directly measure if CheB demethylates only active receptors - rate of methylation drops immediately after addition of ligand indicates that CheB works on active receptors 11