Importance of barrier shape in enzyme-catalyzed reactions: Vibrationally assisted hydrogen tunneling in tryptophan tryptophylquinone-dependent amine dehydrogenases

Jaswir Basran, Shila Patel, Michael J. Sutcliffe, Nigel S. Scrutton

    Research output: Contribution to journalArticlepeer-review

    Abstract

    C-H bond breakage by tryptophan tryptophylquinone (TTQ)-dependent methylamine dehydrogenase (MADH) occurs by vibrationally assisted tunneling (Basran, J., Sutcliffe, M. J., and Scrutton, N. S. (1999) Biochemistry 38, 3218-3222). We show here a similar mechanism in TTQ-dependent aromatic amine dehydrogenase (AADH). The rate of TTQ reduction by dopamine in AADH has a large, temperature independent kinetic isotope effect (KIE = 12.9 ± 0.2), which is highly suggestive of vibrationally assisted tunneling. H-transfer is compromised with benzylamine as substrate and the KIE is deflated (4.8 ± 0.2). The KIE is temperature-independent, but reaction rates are strongly dependent on temperature. With tryptamine as substrate reaction rates can be determined only at low temperature as C-H bond cleavage is rapid, and an exceptionally large KIE (54.7 ± 1.0) is observed. Studies with deuterated tryptamine suggest vibrationally assisted tunneling is the mechanism of deuterium and, by inference, hydrogen transfer. Bond cleavage by MADH using a slow substrate (ethanolamine) occurs with an inflated KIE (14.7 ± 0.2 at 25 °C). The KIE is temperature-dependent, consistent with differential tunneling of protium and deuterium. Our observations illustrate the different modes of H-transfer in MADH and AADH with fast and slow substrates and highlight the importance of barrier shape in determining reaction rate.
    Original languageEnglish
    Pages (from-to)6234-6242
    Number of pages8
    JournalJournal of Biological Chemistry
    Volume276
    Issue number9
    DOIs
    Publication statusPublished - 2 Mar 2001

    Fingerprint

    Dive into the research topics of 'Importance of barrier shape in enzyme-catalyzed reactions: Vibrationally assisted hydrogen tunneling in tryptophan tryptophylquinone-dependent amine dehydrogenases'. Together they form a unique fingerprint.

    Cite this