Lipoxygenase Catalyzed Production of Monools from Linoleates
Matthew Scholten and David G. Rethwisch. Chemical and Biochemical Engineering, University of Iowa, 4133 Seamans Center, Iowa City, IA 52242
It has been well documented that fatty acids including arachidonic acid and linoleic acid can be modified to contain a monoperoxide using lipoxygenases in a buffered aqueous reaction medium. The resulting products display high yields and specifity of the monoperoxide which can than be readily reduced, via a reducing agent such as triphenyl phosphine, to a produce a fatty acid containing a monool. This process is unfeasible on a larger scale because linoleic acid is sparingly soluble in an aqueous environment; typical experiments involve 100 mg linoleic acid per 100 ml of aqueous solvent. In addition, the enzyme is soluble in the aqueous phase and is difficult to recover and recycle. This study focuses on extending the use of lipoxygenases to other molecules specifically methyl linoleate (the methyl ester of linoleic acid) and agricultural oils such as corn oil. The resulting agricultural derivatives and oils containing monool components could be of use in areas such as lubricants and bio-diesel additives. In initial studies soybean lipoxygenase was used to peroxidate a methyl linoleate to contain a monoperoxide in isooctane. Isooctane was initially targeted as a solvent because isooctane gives good solubility of molecular oxygen which is also necessary for the reaction to be successful. Studies have shown that ca. 5-10% conversion was obtained. The majority of this reaction appears to be due to autooxidation and a smaller contribution from enzyme catalysis. Reaction kinetics studies have shown these conversions to happen quickly with no further peroxidation of the methyl linoleate. Reactions have also been attempted in acetone and hexane with limited success for both linoleic acid and methyl linoleate. Future studies could likely involve other organic solvents, biphasic systems, emulsions, lyophilization of the enzyme, and other means to stabilize the enzyme such as immobilization. Through these studies we hope to gain a better understanding of how the enzyme is working in this particular system and determine ways to increase conversion to monoperoxides/monools. Once optimization of this system is complete we hope to extend our studies to agricultural oils, specifically corn oil.