title: Dual positional substrate specificity of rice allene oxide synthase-1: insight into mechanism of inhibition by type II ligand imidazole.
abstract: Phylogenetic and amino acid sequence analysis indicated that rice allene oxide synthase-1 (OsAOS1) is CYP74, and is clearly distinct from CYP74B, C and D subfamilies. Regio- and stereo-chemical analysis revealed the dual substrate specificity of OsAOS1 for (cis,trans)-configurational isomers of 13(S)- and 9(S)-hydroperoxyoctadecadienoic acid. GC-MS analysis showed that OsAOS1 converts 13(S)- and 9(S)-hydroperoxyoctadecadi(tri)enoic acid into their corresponding allene oxide. UV-Visible spectral analysis of native OsAOS1 revealed a Soret maximum at 393 nm, which shifted to 424 nm with several clean isobestic points upon binding of OsAOS1 to imidazole. The spectral shift induced by imidazole correlated with inhibition of OsAOS1 activity, implying that imidazole may coordinate to ferric heme iron, triggering a heme-iron transition from high spin state to low spin state. The implications and significance of a putative type II ligand-induced spin state transition in OsAOS1 are discussed.
authors.affiliation: Department of Molecular Biotechnology and Kumho Life Science Laboratory, College of Agriculture and Life Sciences, Chonnam National University, Gwangju 500-757, Korea.
authors.forename: Sereyvath
authors.initials: S
authors.lastname: Yoeun
authors.forename: Randeep
authors.initials: R
authors.lastname: Rakwal
authors.forename: Oksoo
authors.initials: O
authors.lastname: Han
mesh_terms: D007093:Imidazoles / Q000378:metabolism*; D019746:Intramolecular Oxidoreductases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D007536:Isomerism; D007700:Kinetics; D008024:Ligands; D012275:Oryza / Q000201:enzymology* / Q000235:genetics; D013056:Spectrophotometry, Ultraviolet; D013379:Substrate Specificity
chemical_list: D007093:Imidazoles; D008024:Ligands; D019746:Intramolecular Oxidoreductases; C021377:hydroperoxide isomerase