Hydrogensulfite reductase is an enzyme from the family oxidoreductases and is made up of 4 subtrates:  trithionate, acceptor, H2O, and OH.
This enzyme belongs to the family of oxidoreductases, specifically those acting on a sulfur group of donors with other acceptors. The 4 substrates of this enzyme are trithionate, acceptor, H2O, and OH-, whereas its two products are bisulfite and reduced acceptor. 
