ATPS

ATPS most commonly refers to ATP sulfurylase, an enzyme that initiates the assimilation of inorganic sulfate into organic molecules in many organisms. It catalyzes the activation of sulfate by transferring the gamma-phosphate from ATP to sulfate, forming adenosine-5′-phosphosulfate (APS) and pyrophosphate (PPi).

The biochemical reaction is: sulfate + ATP → APS + PPi. APS can be further phosphorylated by APS kinase to produce 3′-phosphoadenosine-5′-phosphosulfate (PAPS), the activated sulfate donor used in various sulfation reactions and in the biosynthesis of sulfur-containing amino acids such as cysteine.

ATPS is widespread across life and exists in several cellular contexts. In bacteria and archaea, the enzyme is typically cytosolic and encoded by sat or related genes. In plants and algae, plastid-targeted ATPS forms participate in the chloroplast sulfur assimilation pathway. The enzyme supplies activated sulfate for incorporation into biomolecules, while PAPS serves as a sulfate donor for sulfation of carbohydrates, proteins, lipids, and secondary metabolites.

Regulation of ATPS activity reflects cellular sulfur status and may involve transcriptional control and allosteric or redox-based mechanisms, particularly in plants where sulfur metabolism interacts with photosynthesis and stress responses. Understanding ATPS is important for studying sulfur cycling in ecosystems and the metabolic integration of sulfate into essential biomolecules.