= 3'-Phosphoadenylyl sulfate
= PAPS
{c}
{synonym}
\b[3'-Phosphoadenylyl sulfate], abbreviated <PAPS>, is a <nucleotide> used as an activated donor in <sulfation>. Its <adenosine> unit bears <phosphate> groups at the ribose 3′ and 5′ positions; a sulfo group is attached to the 5′ phosphate. That covalent arrangement distinguishes <PAPS> from free <sulfate> dissolved alongside an unrelated <nucleotide>.<3'-phospho-5'-adenylyl sulfate in ChEBI>[CHEBI:17980, Definition, chemical structure and Synonyms.]{ref}
A concrete example is <heparan sulfate glucosamine N-sulfotransferase>. The <enzyme> transfers the sulfur-containing group from <PAPS> to a <glucosamine> nitrogen within <heparan sulfate>, leaving <adenosine 3',5'-bisphosphate>. Abbreviating that product as PAP, the transfer can be summarized schematically as
$$
\mathrm{PAPS}+\text{acceptor}\longrightarrow\mathrm{PAP}+\text{sulfated acceptor}.
$$
This schematic omits proton and charge bookkeeping; the IUBMB reaction specifies the actual polymer-associated acceptor.<Heparan sulfate glucosamine N-sulfotransferase in IUBMB Enzyme Nomenclature>[EC 2.8.2.8, Reaction and Glossary.]{ref}
The example separates donor availability from product specificity. <PAPS> supplies a transferable group, while the <enzyme> determines which acceptor and attachment site participate. Supplying <sulfate> is therefore not, by itself, a specification of which position in a <glycosaminoglycan> becomes modified.
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