Abstract
Kinetic studies have indicated that imidazole is a competitive inhibitor of rice allene oxide synthase‐1 with K i of 34.9, 14.3, 40.3, and 23.3 mM for 13(S)‐HPODE, 13(S)‐HPOTE, 9(S)‐HPODE, and 9(S)‐HPOTE as substrates, respectively. Imidazole‐free rice allene oxide synthase‐1 has a Soret absorbance maximum at 393 nm and occupied high‐spin (g = 6.0) and low‐spin (g = 2.39, 2.24, 1.93) states in the ratio 1:10, as detected by EPR spectroscopy, while in the presence of imidazole the occupancy of the low‐spin state increased to 100%. The results support the hypothesis that imidazole competes with the substrate of allene oxide synthase‐1 for binding to the sixth position of heme iron(III) and that binding of imidazole stabilizes the low‐spin state. The role of detergent binding and implications for the mechanism by which allene oxide synthase‐1 cleaves the RO‐OH bond are discussed.
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