Acetylphosphate

Acetyl phosphate is a reactive acyl phosphate with the formula CH3CO-O-PO3^2-, a mixed anhydride of acetic acid and phosphoric acid. It contains a high-energy linkage that enables transfer of acetyl groups to nucleophiles or transfer of phosphate groups to substrates. In water, acetyl phosphate hydrolyzes to acetate and inorganic phosphate, and it is relatively short-lived under physiological conditions.

In bacteria, acetyl phosphate is produced by phosphotransacetylase from acetyl-CoA and inorganic phosphate: acetyl-CoA + Pi ⇌ acetyl phosphate + CoA. It can be consumed by acetate kinase to form acetate and ATP: acetyl phosphate + ADP → acetate + ATP, providing a route of substrate-level phosphorylation in fermentative or anaerobic metabolism. In some organisms, acetyl phosphate also serves as an intermediate linking acetate production to energy generation.

Beyond metabolism, acetyl phosphate can act as a donor of acetyl groups to proteins in a non-enzymatic process, contributing to lysine acetylation and metabolic regulation. It can also donate a phosphoryl group to histidine residues in bacterial two-component signaling systems, offering a rapid regulatory mechanism that can bypass dedicated histidine kinases under certain conditions.

Because of its reactivity, acetyl phosphate is typically described as a transient metabolite relevant to energy coupling and post-translational modification pathways in prokaryotes. Its cellular levels are tightly regulated, reflecting its roles in metabolism and signaling.