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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 30, Number 4
BKCSDE 30(4)
April 20, 2009 

A Substrate Serves as a Hydrogen Atom Donor in the Enzyme-Initiated Catalytic Mechanism of Dual Positional Specific Maize Lipoxygenase-1
Thavrak Huon, Sungkuk Jang, Kyoungwon Cho, Randeep Rakwal, Je Chang Woo, Ilchul Kim, Seung Wook Chi, Oksoo Han*
Dual positional lipoxygenase, Enzyme-initiated mechanism, Kinetic control, Thermodynamic control, Radical mechanism
The maize lipoxgyenase-1 is a non-traditional dual positional specific enzyme and the reaction proceeds via enzyme-initiated catalysis. Bioinformatic analysis indicated that the maize lipoxygenase-1 is structurally more similar to soybean LOX1 than pea LOXN2 in that it has an additional external loop (residues 318-351) in the carboxy-terminal catalytic domain. We analyzed the dependence of product distribution on concentration of linoleic acid and monitored the formation of hydroperoxyoctadecadienoic acid as a function of enzyme concentration. Product distribution was strongly influenced by substrate concentration, such that kinetically-controlled regioisomers were enriched and thermodynamically-controlled regioisomers were depleted at high substrate concentration. Kinetic studies indicated that the formation of hydroperoxyoctadecadienoic acid saturated rapidly in an enzyme concentration-dependent manner, which implied that reactivation by reoxidation of inactive Fe(II) failed to occur. Our results support the previously proposed enzyme-initiated catalytic mechanism of the maize lipoxgyenase-1 and reveals that a substrate molecule serves as a hydrogen atom donor in its enzyme-initiated catalysis.
917 - 923
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