The many flavoproteins that catalyze oxidation of carbon-nitrogen and carbon-oxygen bonds by transferring a hydride equivalent to the flavin play critical roles throughout metabolism. A number of these enzymes are targets for treatment of major diseases, so that better understanding of their mechanisms could provide insight for development of therapeutic agents. These enzymes also belong to multiple structural families;it is unclear if this reflects multiple strategies to catalyze essentially identical reactions or is a example of convergent evolution. We have interpreted previous studies of alcohol, keto acid, and amino acid oxidizing enzymes as consistent with a common hydride transfer mechanism for all, with CN and CO bond oxidizing enzymes differing in the need for an active site base in the latter. We now propose to carry out experiments to determine if enzymes that oxidize simple amines and polyamines utilize this same mechanism despite differences in protein and substrate structure. We will determine the mechanism of L- hydroxy-nicotine oxidase, an enzyme in the monoamine oxidase structural family that is proposed to catalyze the oxidation of a carbon-carbon bond rather than a carbon-nitrogen bond. We will continue our studies of polyamine oxidases, enzymes that oxidize the same substrates with different substrate specificities. 15N and 13C kinetic isotope effects will be used to determine the mechanism of amine oxidation, and analysis of the effects of site-directed mutations combined with crystallography will be used to determine the structural basis for the different specificities. We will measure 13C isotope effects for two structural classes of flavin amine oxidases to better define their transition state structures and to provide baseline values for other structural familis. We will determine if members of the trimethylamine dehydrogenase structural family use the same mechanism for amine oxidation as other structural families of amine-oxidizing enzymes. The results of these experiments will test our hypothesis that the different structural families of amine oxidizing flavoenzymes are examples of convergent evolution on a common catalytic mechanism, potentially providing a unifying mechanism for a structurally divergent group of enzymes. Finally, we will initiate studies of the oxidative reactions of flavin-dependent amine oxidases, to probe for intermediates in the reaction and for oxygen-binding sites.

Public Health Relevance

Flavoproteins oxidation that catalyze of amines play central roles in metabolism and are thus frequent targets of drugs. The experiments proposed here will provide fundamental insights into the relationship of protein structure to mechanism and binding specificity for this large group of enzymes. The results will be useful in the design of specific drugs targeting individual enzymes and of new enzymes that catalyze synthetically useful reactions.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
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Macromolecular Structure and Function A Study Section (MSFA)
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Barski, Oleg
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University of Texas Health Science Center San Antonio
Schools of Medicine
San Antonio
United States
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Fitzpatrick, Paul F (2015) Combining solvent isotope effects with substrate isotope effects in mechanistic studies of alcohol and amine oxidation by enzymes. Biochim Biophys Acta 1854:1746-55
Roberts, Kenneth M; Tormos, José R; Fitzpatrick, Paul F (2014) Characterization of unstable products of flavin- and pterin-dependent enzymes by continuous-flow mass spectrometry. Biochemistry 53:2672-9
Gaweska, Helena M; Taylor, Alexander B; Hart, P John et al. (2013) Structure of the flavoprotein tryptophan 2-monooxygenase, a key enzyme in the formation of galls in plants. Biochemistry 52:2620-6
Gaweska, Helena; Fitzpatrick, Paul F (2011) Structures and Mechanism of the Monoamine Oxidase Family. Biomol Concepts 2:365-377
Tormos, Jose R; Taylor, Alexander B; Daubner, S Colette et al. (2010) Identification of a hypothetical protein from Podospora anserina as a nitroalkane oxidase. Biochemistry 49:5035-41
Adachi, Mariya S; Juarez, Paul R; Fitzpatrick, Paul F (2010) Mechanistic studies of human spermine oxidase: kinetic mechanism and pH effects. Biochemistry 49:386-92
Valley, Michael P; Fenny, Nana S; Ali, Shah R et al. (2010) Characterization of active site residues of nitroalkane oxidase. Bioorg Chem 38:115-9
Fitzpatrick, Paul F (2010) Oxidation of amines by flavoproteins. Arch Biochem Biophys 493:13-25
Henderson Pozzi, Michelle; Fitzpatrick, Paul F (2010) A lysine conserved in the monoamine oxidase family is involved in oxidation of the reduced flavin in mouse polyamine oxidase. Arch Biochem Biophys 498:83-8
Pozzi, Michelle Henderson; Gawandi, Vijay; Fitzpatrick, Paul F (2009) Mechanistic studies of para-substituted N,N'-dibenzyl-1,4-diaminobutanes as substrates for a mammalian polyamine oxidase. Biochemistry 48:12305-13

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