Catalytic Properties of Rice α-Oxygenase A COMPARISON WITH MAMMALIAN PROSTAGLANDIN H SYNTHASES

摘要: Abstract Long-chain fatty acids can be metabolized to Cn −1 aldehydes by α-oxidation in plants. The reaction mechanism of the enzyme has not been elucidated. In this study, a complete nucleotide sequence acid α-oxygenase gene rice plants (Oryza sativa) was isolated. deduced amino showed some similarity with those mammalian prostaglandin H synthases (PGHSs). expressed Escherichia coli and purified apparently homogenous state. It highest activity linoleic predominantly formed 2-hydroperoxide (Cn), which is then spontaneously decarboxylated form corresponding aldehyde. With or as substrate, no product having aλ max at approximately 234 nm, indicated that could oxygenize pentadiene system substrate. spectroscopic feature its ferrous state similar PGHS, whereas dithionite-reduced significant difference. Site-directed mutagenesis revealed His-158, Tyr-380, Ser-558 were essential for activity. These residues are conserved PGHS known heme ligand, source radical species initiate oxygenation residue involved substrate binding, respectively. This finding suggested initial step high PGHS. inhibited imidazole but hardly nonsteroidal anti-inflammatory drugs, such aspirin, ibuprofen, flurbiprofen, typical inhibitors. addition, peroxidase detected when palmitic used From these findings, catalytic resemblance between seems evident, although there still differences their recognitions peroxidation activities.