Mechanism of alkane formation by cyanobacterial aldehyde decarbonylase

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In this award from the Chemistry of Life Processes in the Chemistry Division, Dr. E. Neil Marsh, from the University of Michigan, will elucidate the mechanism of a newly-discovered hydrocarbon-forming enzyme from cyanobacteria, aldehyde decarbonylase (cAD). Biosynthetic pathways that generate hydrocarbons have become the subject of intense interest recently as their potential to generate new biofuels has been recognized. Aldehyde decarbonylase is a member of a well-studied class of enzymes, the non-heme di-iron dioxygenases. Preliminary studies have shown that cAD catalyzes a most unusual reaction involving the conversion of long-chain fatty aldehydes to the corresponding alkanes and formate. To investigate the mechanism, alternative substrates that may act as mechanism-based inhibitors will be synthesized to gain evidence for proposed radical intermediates in the reaction. The role of the reducing system in the reaction will be investigated and the components of the native reducing system in the host cyanobacterium P. marinus, will be identified. Site-directed mutagenesis will be used to investigate the role of active site residues in determining substrate specificity and controlling the mechanism of the reaction. Lastly, kinetic isotope effects will be measured to provide insight into the rate determining step in cAD and the nature of the transition state leading to carbon-carbon bond cleavage.There is a pressing need to develop new pathways to produce biofuels based on hydrocarbons as sustainable alternatives to fossil fuels. The cyanobacterial enzyme aldehyde decarbonylase produces hydrocarbons and has attracted particular interest for biofuels applications; yet its extremely low activity presents a major stumbling block to its use. Understanding how the enzyme works is the first step to designing better enzymes, or synthetic catalysts, that accomplish the synthesis of hydrocarbons more efficiently. This, in turn, may allow the development of new routes to biofuels that can substitute for current fossil fuels including gasoline, diesel and jet fuels.