CysH (Phosphoadenosine phosphosulfate reductase) belongs to the PAPS reductase family, specifically those acting on a sulfur group of donors with a disulfide as acceptor. In enzymology, a cysH is an enzyme that catalyzes the chemical reaction. Three substrates of this enzyme are adenosine 3',5'-bisphosphate, sulfite, and thioredoxin disulfide, whereas its two products are 3'-phosphoadenylyl sulfate and thioredoxin.