adenosine3phosphosulfate

Adenosine-3'-phosphosulfate, often abbreviated as APS, is a naturally occurring nucleotide derivative that plays a crucial role in biological sulfate assimilation. It is an intermediate in the pathway by which many organisms, including bacteria, fungi, and plants, convert inorganic sulfate into organic sulfur-containing compounds. In these organisms, APS is synthesized from ATP and inorganic sulfate. The enzyme ATP sulfurylase catalyzes this reaction, yielding APS and pyrophosphate.

APS serves as a high-energy sulfate donor. In the subsequent step of sulfate assimilation, APS is typically phosphorylated by APS kinase to form adenosine-3',5'-bisphosphate (PAPS). PAPS is the primary activated sulfate donor for a vast array of sulfotransferases, enzymes that catalyze the transfer of a sulfate group to various acceptor molecules. These sulfated molecules are essential for numerous biological functions, including the synthesis of amino acids like cysteine and methionine, the formation of polysaccharides, and the modification of proteins and lipids.

While APS is a key intermediate, its direct role as a sulfate donor is less common than that of PAPS. However, in some specific metabolic pathways, APS itself can directly transfer its sulfate group. The precise balance and regulation of APS and PAPS synthesis and utilization are critical for maintaining cellular sulfur homeostasis and supporting vital metabolic processes.