Microsecond reaction kinetics and catalytic mechanism of bacterial cytochrome oxidases

Angela Paulus

    Research output: ThesisDissertation (TU Delft)

    45 Downloads (Pure)

    Abstract

    Fundamental biochemical research is of crucial importance for a complete and detailed
    understanding of what drives enzyme activity and how enzyme kinetic properties are
    optimized towards survival of the host organism. When cells fail to produce a fully functional
    enzyme, the organism’s ability to survive or thrive is impacted. In humans, for example, low
    levels or absence of lactase causes lactose intolerance, while decreased performance of the
    proton-pumping enzyme cytochrome aa3 oxidase in the mithochondrial electron transport
    chain in brain cells is linked to Alzheimer’s disease.
    Direct observation of all steps of the catalytic cycle of bacterial oxidoreductases is
    challenging, since a full turnover of these enzymes typically takes only ~1 ms. Through
    targeted mutagenesis of enzymes it is possible to create variants of an enzyme that can only
    catalyze part of the reaction, or that will perform the entire reaction, yet with different
    kinetics of the individual reaction steps, providing clues as to what drives or limits the
    enzymatic reaction. Hypotheses based on observations with mutated enzyme variants can be
    proven or disproven by studying the wildtype uncorrupted enzyme under mild conditions,
    minimizing artefacts introduced by working in vitro. The stopped-flow spectrophotometer is
    a valuable tool for kinetic analysis of enzyme reactions, but does not offer the time resolution
    required to resolve early pre-steady state kinetics. The microsecond freeze-hyperquenching
    setup (MHQ), on the other hand, is able to create ‘snapshot’ samples of enzymes during
    catalytic turnover at reaction times down to 74 μs. The quenched samples can be subjected to
    further analysis by UV-vis or EPR spectroscopy. This thesis decribes the kinetic study of
    three bacterial oxidoreductases and makes the comparison between the catalytic mechanisms
    of oxygen reduction (and proton pumping) of each of the three enzymes.
    Original languageEnglish
    Supervisors/Advisors
    • de Vries, Simon, Supervisor
    • Hagen, W.R., Supervisor
    Award date12 May 2017
    Print ISBNs978-94-028-0630-4
    DOIs
    Publication statusPublished - 2017

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