Acetyl phosphate and the activation of two-component response regulators

Several bacterial response regulator proteins (CheY, NR(I), PhoB, and OmpR) become phosphorylated in vitro when incubated with acetyl phosphate. In the presence of high levels of acetyl phosphate and Mg²⁺, CheY reached steady state phosphorylation in less than 30 s; NR(I) and PhoB reached steady state more slowly (t 1/2 ) to steady state of 1.5 and >15 min, respectively). A simple method was developed to measure acetyl phosphate levels in Escherichia coli grown in defined media. Levels of acetyl phosphate were elevated in cells grown in pyruvate, glucose, and glucuronic acid and were low in cells grown in fructose, glycerol, and fumarate. The effects of varying the intracellular amounts of acetyl phosphate on chemotaxis and the osmo-response were also investigated. Acetyl phosphate was not required but did influence each of these responses. These results suggest that acetyl phosphate may influence either the sensitivity or the magnitude of an adaptive response.