adenosin5fosfosulfat

Adenosine-5'-phosphosulfate, commonly abbreviated APS, is a nucleotide-sulfate intermediate central to sulfur metabolism. It consists of the ribonucleoside adenosine with a phosphate group at the 5' position that is esterified to a sulfate group, yielding adenosine-5'-phosphosulfate.

APS is formed when sulfate is activated by ATP sulfurylase, converting ATP and sulfate into APS and ADP. In many organisms, APS can follow two main routes: it can be reduced by APS reductase to sulfite for incorporation into cysteine and other sulfur-containing molecules, or it can be phosphorylated by APS kinase to form 3'-phosphoadenosine-5'-phosphosulfate (PAPS), a universal sulfate donor for sulfation reactions. In animals and fungi, a bifunctional enzyme called PAPSS (PAPS synthase) conducts both steps, producing PAPS in the cytosol.

As a key metabolic intermediate, APS sits at a branch point between assimilatory reduction to sulfite and sulfation to PAPS. PAPS transfers sulfate groups to a wide range of substrates via sulfotransferases, sulfating molecules such as proteins, glycosaminoglycans, lipids, hormones, and xenobiotics. The sulfation reactions generate 3'-phosphoadenosine-5'-phosphate (PAP) as a byproduct, which is subsequently recycled or degraded.

Chemical and physiological properties of APS reflect its role as a highly polar, negatively charged nucleotide-sulfate. It is typically found in the cytosol and other aqueous compartments and does not cross membranes readily without specific transport systems.

In summary, APS is a crucial intermediate in sulfur activation and transfer, linking sulfate assimilation with the various sulfation pathways that modify biological macromolecules and small molecules.