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Cinnamyl alcohol dehydrogenases (CAD; 1.1.1.195) catalyse the reversible conversion of p-hydroxycinnamaldehydes to their corresponding alcohols, leading to the biosynthesis of lignin in plants. Outside of plants their role is less defined. The gene for cinnamyl alcohol dehydrogenase from Helico-bacter pylori(HpCAD) was cloned in Escherichia coliand the recombinant enzyme characterized for substrate specificity. The enzyme is a monomer of 42.5 kDa found predominantly in the cytosol of the bacterium | ềFEBS Journal Characterization of cinnamyl alcohol dehydrogenase of Helicobacter pylori An aldehyde dismutating enzyme Blanaid Mee1 Dermot Kelleher2 Jesus Frias1 Renee Malone1 Keith F. Tipton3 Gary T.M. Henehan1 and Henry J. Windle2 1 Schoolof Food Science and EnvironmentalHealth Dublin Institute of Technology Ireland 2 Department of ClinicalMedicine Trinity College Dublin Ireland 3 Department of Biochemistry Trinity College Dublin Ireland Keywords aldehyde cinnamylalcoholdehydrogenase dismutation Helicobacter pylori lignin Correspondence G. Henehan Schoolof Environmental Health and Food Science Dublin Institute of Technology Ireland E-mail Gary.Henehan@DIT.ie Received 17 November 2004 revised 6 January 2005 accepted 7 January 2005 doi 10.1111 j.1742-4658.2005.04561.x Cinnamyl alcohol dehydrogenases CAD 1.1.1.195 catalyse the reversible conversion of p-hydroxycinnamaldehydes to their corresponding alcohols leading to the biosynthesis of lignin in plants. Outside of plants their role is less defined. The gene for cinnamyl alcohol dehydrogenase from Helicobacter pylori HpCAD was cloned in Escherichia coli and the recombinant enzyme characterized for substrate specificity. The enzyme is a monomer of 42.5 kDa found predominantly in the cytosol of the bacterium. It is specific for NADP H as cofactor and has a broad substrate specificity for alcohol and aldehyde substrates. Its substrate specificity is similar to the well-characterized plant enzymes. High substrate inhibition was observed and a mechanism of competitive inhibition proposed. The enzyme was found to be capable of catalysing the dismutation of benzaldehyde to benzyl alcohol and benzoic acid. This dismutation reaction has not been shown previously for this class of alcohol dehydrogenase and provides the bacterium with a means of reducing aldehyde concentration within the cell. Cinnamyl alcohol dehydrogenases CAD EC 1.1.1.195 are zinc dependent dehydrogenases and are among the least studied of the alcohol .
