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Hydroxymethylated Dioxobilins in Senescent Arabidopsis thaliana Leaves: Sign of a Puzzling Biosynthetic Intermezzo of Chlorophyll Breakdown
Authors:Iris Süssenbacher  Dr Christoph R Kreutz  Dr Bastien Christ  Prof?Dr Stefan Hörtensteiner  Prof?Dr Bernhard Kräutler
Institution:1. Institute of Organic Chemistry and Center for Molecular Biosciences, University of Innsbruck, Innrain 80/82, 6020 Innsbruck (Austria);2. Institute of Plant Biology, University of Zürich, Zollikerstrasse 107, 8008 Zürich (Switzerland)
Abstract:1‐Formyl‐19‐oxobilin‐type tetrapyrroles are characteristic, abundant products of chlorophyll breakdown in senescent leaves. However, in some leaves, 1,19‐dioxobilin‐type chlorophyll catabolites (DCCs) lacking the formyl group accumulate instead. A P450 enzyme was identified in in vitro studies that removed the formyl group of a primary fluorescent chlorophyll catabolite (pFCC) and generated fluorescent DCCs. These DCCs are precursors of isomeric nonfluorescent DCCs (NDCCs). Here, we report a structural investigation of the NDCCs in senescent leaves of wild‐type Arabidopsis thaliana. Four new NDCCs were characterized, two of which carried a stereoselectively added hydroxymethyl group. Such formal DCC hydroxymethylations were previously found in DCCs in leaves of a mutant of A. thaliana. They are now indicated to be a feature of chlorophyll breakdown in A. thaliana, associated with the specific in vivo deformylation of pFCC en route to NDCCs.
Keywords:biosynthesis  chlorophyll  phyllobilin  structure elucidation  tetrapyrrole
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