Date of Award

2016

Document Type

Open Access Dissertation

Department

Chemistry and Biochemistry

Sub-Department

College of Arts and Sciences

First Advisor

Thomas M. Makris

Abstract

OleT (CYP152L1) is a recently discovered cytochrome P450 that is structurally similar to peroxide dependent P450s that catalyze fatty acid hydroxylations. OleT has been shown to catalyze the cleavage of n chain length fatty acids to form n-1 alkenes through C-C bond scission of the terminal carboxylate. Using headspace GC-MS and FTIR with isotopically labeled substrates, we have confirmed that OleT metabolizes eicosanoic acid to 1-nonadecene, forming carbon dioxide (CO2) as a co-product of the reaction. No oxygen deriving from peroxide is observed in either product. In order to probe the mechanistic deviation of OleT from P450 peroxygenases, we have employed a “decoy” approach where a short chain length fatty acid provides the acidic group necessary for peroxide heterolysis, and also allows access of small molecule probe substrates. Using this approach, we confirm that OleT also catalyzes epoxidation and hydroxylation reactions. Products derived from the metabolism of radical clock substrates directly show that OleT is capable of efficient oxygen rebound with radical lifetimes that are similar to other P450 monooxygenases. A site-directed mutant, in which the acidic group is instead provided by the protein framework, circumvents the need for a substrate carboxylate, and shows efficient metabolism of a wide range of hydrocarbon substrates. In addition, we described efforts to leverage OleT for electron driven hydrocarbon production, replacing H2O2 with a non-conventional redox partner or a Ru(II) photosensitizer covalently attached to a non-native surface cysteine.Last but not least, the development of a general and facile colorimetric optical assay for the detection of carbondioxide (CO2) generated from enzymatic reactions is described. The assay utilize the use of natural abundant of carbonic anhydrases, and a readily available pH indicator (ex. bromothymol blue) for the monitoring of pH changes induced by the release of CO2 using a standard UV-vis spectrophotometer. This optical method can accurately and reliably quantify CO2 produced from two entirely different class of enzymes: α-ketoglutarate-dependent dioxygenases and cytochrome P450 OleT decarboxylases

Rights

© 2016, Chun H. Hsieh

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