title: A possible role for the chloroplast pyruvate dehydrogenase complex in plant glycolate and glyoxylate metabolism.
abstract: Glyoxylate is a peroxisomal intermediate of photorespiration, the recycling pathway for 2-phosphoglycolate (2-PG) produced by the oxygenase activity of Rubisco. Under hot and dry growth conditions, photorespiratory intermediates can accumulate and must be detoxified by alternative pathways, including plastidal reactions. Moreover, there is evidence that chloroplasts are capable of actively producing glyoxylate from glycolate. Further metabolic steps are unknown, but probably include a CO2 release step. Here, we report that CO2 production from glycolate and glyoxylate in isolated tobacco chloroplasts can be inhibited by pyruvate, but not related compounds. We isolated a protein fraction that was enriched for the chloroplast pyruvate dehydrogenase complex (PDC). The fraction contained a protein complex of several MDa in size that included all predicted subunits of the chloroplast PDC and a so far unidentified HSP93-V/ClpC1 heat shock protein. Glyoxylate competitively inhibited NADH formation from pyruvate in this fraction. The Km for pyruvate and the Ki for glyoxylate were 330 and 270 μM, respectively. Glyoxylate decarboxylation was also enriched in this fraction and could be in turn inhibited by pyruvate. Based on these data, we suggest that the chloroplast PDC might be part of a pathway for glycolate and/or glyoxylate oxidation in chloroplasts.
authors.affiliation: Leibniz University Hannover, Institute of Botany, D 30419 Hannover, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Blume
authors.forename: Christof
authors.initials: C
authors.lastname: Behrens
authors.forename: Holger
authors.initials: H
authors.lastname: Eubel
authors.forename: Hans-Peter
authors.initials: HP
authors.lastname: Braun
authors.forename: Christoph
authors.initials: C
authors.lastname: Peterhansel
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism*; D019069:Cell Respiration; D002736:Chloroplasts / Q000201:enzymology / Q000378:metabolism*; D003653:Decarboxylation; D006016:Glycolates / Q000378:metabolism*; D006038:Glyoxylates / Q000378:metabolism*; D006360:Heat-Shock Proteins / Q000378:metabolism; D007700:Kinetics; D009243:NAD / Q000096:biosynthesis; D010788:Photosynthesis; D011768:Pyruvate Dehydrogenase Complex / Q000378:metabolism*; D019289:Pyruvic Acid / Q000378:metabolism*; D012273:Ribulose-Bisphosphate Carboxylase / Q000378:metabolism; D014026:Nicotiana / Q000201:enzymology / Q000378:metabolism*
chemical_list: D006016:Glycolates; D006038:Glyoxylates; D006360:Heat-Shock Proteins; D011768:Pyruvate Dehydrogenase Complex; D009243:NAD; C031149:glycolic acid; D002245:Carbon Dioxide; D019289:Pyruvic Acid; D012273:Ribulose-Bisphosphate Carboxylase; C013193:phosphoglycolate; C031150:glyoxylic acid
keywords: 2D-BN/SDS–PAGE; Heat shock protein Hsp93-V; PDC; Photorespiration; TPP; Two-dimensional BN/SDS–PAGE; pyruvate dehydrogenase complex; thiamine pyrophosphate; two dimensional blue native SDS–PAGE