Novel prenylated hemes as cofactors of cytochrome oxidases. Archaea have modified hemes A and O.

A series of novel hemes with modifications of the isoprenyl side chain has been detected in archaea. Heme A(S) was isolated from cytochrome oxidases of the thermoacidophilic archaeon, Sulfolobus acidocaldarius. Heme A(S) has the same spectroscopic features as heme A but has a hydroxyethylgeranylgeranyl side chain instead of the hydroxyethylfarnesyl group. This variant is also present in other archaeal oxidases as well as in the cytochrome oxidases of a thermophilic eubacterium. Other archaea (Thermoplasma, Pyrobaculum) were also shown to have cytochrome oxidases. From these organisms, three novel prenylated heme variants (called OT, OP1, and OP2) were isolated. They are structurally related to heme O; OP2 has a hydroxyethylgeranylgeranyl instead of the hydroxyethylfarnesyl side chain. In OP1 and OT, the hydroxyethylprenyl group is altered to ethenylprenyl by elimination of a water molecule. Most probably, the novel hemes are cofactors binding to the binuclear reaction centers of archaeal cytochrome oxidases.