PAPS: Products3'-Phosphoadenosine-5'-phosphosulfate (PAPS) is the
universal sulfur donor for sulfotransferases. It is synthesized
from ATP through two steps. In the first step, one ATP
molecule is converted to adenosine-5'-phosphosulfate (APS)
by ATP sulfurylase and pyrophosphate (PPi) is generated as
a byproduct. In the second step, the APS is converted to
PAPS by APS kinase and ADP is generated as a byproduct.
To drive the reaction forward, the pyrophosphate can be
further degraded to phosphate (Pi) by inorganic
pyrophosphatase to eliminate feedback inhibition, and the
ADP can be converted back to ATP using pyruvate kinase.