title: Thioredoxin-mediated reversible dissociation of a stromal multiprotein complex in response to changes in light availability.
abstract: A Calvin cycle multiprotein complex including phosphoribulokinase (PRK), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and a small protein, CP12, has previously been identified. In this article, we have studied this complex in leaves and have shown that dissociation and reassociation of the PRK/GAPDH/CP12 complex occurs in a time frame of minutes, allowing for rapid regulation of enzyme activity. Furthermore, we have shown that the extent of formation and dissociation of the PRK/GAPDH/CP12 complex correlates with the quantity of light. These data provide evidence linking the status of this complex with the rapid and subtle regulation of GAPDH and PRK activities in response to fluctuations in light availability. We have also demonstrated that dissociation of this complex depends on electron transport chain activity and that the major factor involved in the dissociation of the pea complex was thioredoxin f. We show here that both PRK and GAPDH are present in the reduced form in leaves in the dark, but are inactive, demonstrating the role of the PRK/GAPDH/CP12 complex in deactivating these enzymes in response to reductions in light intensity. Based on our data, we propose a model for thioredoxin f-mediated activation of PRK and GAPDH by two mechanisms: directly through reduction of disulfide bonds within these enzymes and indirectly by mediating the breakdown of the complex in response to changes in light intensity.
authors.affiliation: Department of Biological Sciences, University of Essex, Wivenhoe Park, Colchester, Essex CO4 3SQ, United Kingdom.
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Howard
authors.forename: Metodi
authors.initials: M
authors.lastname: Metodiev
authors.forename: Julie C
authors.initials: JC
authors.lastname: Lloyd
authors.forename: Christine A
authors.initials: CA
authors.lastname: Raines
mesh_terms: D002244:Carbon / Q000378:metabolism; D002457:Cell Extracts; D002736:Chloroplasts / Q000201:enzymology* / Q000528:radiation effects*; D004579:Electron Transport / Q000528:radiation effects; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases / Q000378:metabolism; D008027:Light; D046912:Multiprotein Complexes / Q000378:metabolism*; D018532:Pisum sativum / Q000201:enzymology* / Q000528:radiation effects*; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism; D010788:Photosynthesis / Q000528:radiation effects; D010940:Plant Proteins / Q000302:isolation & purification / Q000378:metabolism; D013879:Thioredoxins / Q000378:metabolism*
chemical_list: D002457:Cell Extracts; D046912:Multiprotein Complexes; D010940:Plant Proteins; D013879:Thioredoxins; D002244:Carbon; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases; D017853:Phosphotransferases (Alcohol Group Acceptor); C022390:phosphoribulokinase