May be involved in sulfur metabolism and oxidative stress response. Does not show RuBisCO activity (By similarity). Binds 1 Mg(2+) ion per subunit. Homodimer. Belongs to the RuBisCO large chain family. Type IV subfamily. Although strongly related to RuBisCO family, it lacks the conserved Lys active site in position 327, which is replaced by an Arg residue, suggesting that it may catalyze enolization but not carboxylation.