Ligand binding to cytochrome c peroxidase from Pseudomonas aeruginosa

The high potential heme site of Pseudomonas cytochrome c peroxidase has His and Met as ligands. On reduction, the Fe-met bond becomes photosensitive. Following photolysis, the bond reforms with a half-time of 35 ps. The low potential heme peroxidatic site of the fully reduced enzyme has been shown to bind to a range of ligands. The compounds with carbon monoxide, methyl, ethyl, n-butyl, and t-butyl isonitriles have been investigated by laser flash photolysis. All are photosensitive and show different degrees of geminate recombination of ligand in the picosecond and nanosecond time ranges. Carbon monoxide shows the least effect. The three straight-chain isonitriles show about 50% geminate recombination with half-times of the order of 10 ns. t-Butyl isonitrile shows more and faster recombination. These results imply considerable freedom of movement within the active site for the smaller ligands.