Analysis of 1-deoxy-d-xylulose 5-phosphate synthase activity in Grey poplar leaves using isotope ratio mass spectrometry |
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Authors: | Andrea Ghirardo Ina Zimmer Nicolas Brüggemann Jörg-Peter Schnitzler |
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Institution: | Karlsruhe Institute of Technology (KIT), Institute of Meteorology and Climate Research (IMK-IFU), Kreuzeckbahnstrasse 19, 82467 Garmisch-Partenkirchen, Germany |
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Abstract: | Deoxy-xylulose phosphate synthase (DXS) catalyzes the first step of the methylerythritol phosphate (MEP) pathway and it might regulate the metabolic flux in plastidic isoprenoid biosynthesis. We developed a sensitive assay suitable for plant extracts that is based on the decarboxylation of labeled pyruvate (1-13C)-PYR and detection of 13CO2 by isotope ratio mass spectrometry. We tested our method investigating the DXS activity in poplar leaves. Apparent DXS activity showed Michaelis constants of 111 and 158 μM for glyceraldehyde phosphate and pyruvate, respectively; pH and temperature optima were found at pH 8.6 and 45 °C. DXS activity was inhibited when the competitive inhibitor β-fluoropyruvate was added to the reaction mixture. DXS activity strongly depended on leaf development with higher activity in young leaves and correlated fairly well with leaf isoprene emission potential. In mature poplar leaves, isoprene emission is the main metabolic sink of plastidic isoprenoid intermediates. Consequently, we found lower DXS activity in non-isoprene-emitting lines of poplar than in emitting plants as indicator of a lower demand of metabolic flux within the MEP pathway. |
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