title: Kinetic characterization and regulation of the human retinaldehyde dehydrogenase 2 enzyme during production of retinoic acid.
abstract: Retinoic acid (RA) is an important regulator of embryogenesis and tissue homoeostasis. Perturbation of RA signalling causes developmental disorders, osteoarthritis, schizophrenia and several types of tumours. RA is produced by oxidation of retinaldehyde from vitamin A. The main enzyme producing RA in the early embryo is retinaldehyde dehydrogenase 2 (RALDH2, ALDH1A2). In the present study we describe in depth the kinetic properties and regulation of the human RALDH2 (hRALDH2) enzyme. We show that this enzyme produces RA using in vivo and in vitro assays. We studied the naturally occurring all-trans-, 9-cis- and 13-cis-retinaldehyde isomers as substrates of hRALDH2. Based on the values measured for the Michaelis-Menten constant Km and the maximal rate Vmax, in vitro hRALDH2 displays the same catalytic efficiency for their oxidation. We characterized two known inhibitors of the vertebrate RALDH2 and determined their kinetic parameters on hRALDH2. In addition, RA was studied as a possible inhibitor of hRALDH2 and a regulator of its activity. We show that hRALDH2 is not inhibited by its oxidation product, all-trans-RA, suggesting the absence of a negative feedback regulatory loop. Expression of the Raldh2 gene is known to be regulated by RA itself, suggesting that the main regulation of the hRALDH2 activity level is transcriptional.
authors.affiliation: Department of Developmental Biology and Cancer Research, Institute for Medical Research Israel-Canada, Faculty of Medicine, Hebrew University of Jerusalem, Jerusalem, Israel.
authors.forename: Yehuda
authors.initials: Y
authors.lastname: Shabtai
authors.affiliation: Department of Genetics, Alexander Silberman Institute of Life Sciences, Faculty of Science, Hebrew University of Jerusalem, Jerusalem, Israel.
authors.forename: Halim
authors.initials: H
authors.lastname: Jubran
authors.affiliation: Institute for Drug Research, School of Pharmacy, Faculty of Medicine, Hebrew University of Jerusalem, Jerusalem, Israel.
authors.forename: Taher
authors.initials: T
authors.lastname: Nassar
authors.affiliation: Department of Genetics, Alexander Silberman Institute of Life Sciences, Faculty of Science, Hebrew University of Jerusalem, Jerusalem, Israel.
authors.forename: Joseph
authors.initials: J
authors.lastname: Hirschberg
authors.affiliation: Department of Developmental Biology and Cancer Research, Institute for Medical Research Israel-Canada, Faculty of Medicine, Hebrew University of Jerusalem, Jerusalem, Israel abrahamf@ekmd.huji.ac.il.
authors.forename: Abraham
authors.initials: A
authors.lastname: Fainsod
mesh_terms: D000080924:Aldehyde Dehydrogenase 1 Family; D018076:DNA, Complementary / Q000235:genetics; D057075:Enzyme Assays; D006801:Humans; D007700:Kinetics; D060888:Real-Time Polymerase Chain Reaction; D050697:Retinal Dehydrogenase / Q000235:genetics / Q000378:metabolism*; D012172:Retinaldehyde / Q000378:metabolism; D013379:Substrate Specificity; D014212:Tretinoin / Q000378:metabolism*; D001616:beta-Galactosidase / Q000378:metabolism
chemical_list: D018076:DNA, Complementary; D014212:Tretinoin; D000080924:Aldehyde Dehydrogenase 1 Family; C545372:ALDH1A2 protein, human; D050697:Retinal Dehydrogenase; D001616:beta-Galactosidase; D012172:Retinaldehyde
keywords: ALDH1A2; enzyme kinetics; retinaldehyde dehydrogenase; retinoic acid signalling; vitamin A metabolism