Send to

Choose Destination
See comment in PubMed Commons below
Biochemistry. 2014 Apr 1;53(12):2007-16. doi: 10.1021/bi401256b. Epub 2014 Mar 19.

How pH modulates the reactivity and selectivity of a siderophore-associated flavin monooxygenase.

Author information

Department of Chemistry and Biochemistry, University of Notre Dame , Notre Dame, Indiana 46556, United States.


Flavin-containing monooxygenases (FMOs) catalyze the oxygenation of diverse organic molecules using O2, NADPH, and the flavin adenine dinucleotide (FAD) cofactor. The fungal FMO SidA initiates peptidic siderophore biosynthesis via the highly selective hydroxylation of L-ornithine, while the related amino acid L-lysine is a potent effector of reaction uncoupling to generate H2O2. We hypothesized that protonation states could critically influence both substrate-selective hydroxylation and H2O2 release, and therefore undertook a study of SidA's pH-dependent reaction kinetics. Consistent with other FMOs that stabilize a C4a-OO(H) intermediate, SidA's reductive half reaction is pH independent. The rate constant for the formation of the reactive C4a-OO(H) intermediate from reduced SidA and O2 is likewise independent of pH. However, the rate constants for C4a-OO(H) reactions, either to eliminate H2O2 or to hydroxylate L-Orn, were strongly pH-dependent and influenced by the nature of the bound amino acid. Solvent kinetic isotope effects of 6.6 ± 0.3 and 1.9 ± 0.2 were measured for the C4a-OOH/H2O2 conversion in the presence and absence of L-Lys, respectively. A model is proposed in which L-Lys accelerates H2O2 release via an acid-base mechanism and where side-chain position determines whether H2O2 or the hydroxylation product is observed.

[Indexed for MEDLINE]
Free PMC Article
PubMed Commons home

PubMed Commons

How to join PubMed Commons

    Supplemental Content

    Full text links

    Icon for American Chemical Society Icon for PubMed Central
    Loading ...
    Support Center