title: Rubisco in planta kcat is regulated in balance with photosynthetic electron transport.
abstract: Site turnover rate (k(cat)) of Rubisco was measured in intact leaves of different plants. Potato (Solanum tuberosum L.) and birch (Betula pendula Roth.) leaves were taken from field-growing plants. Sunflower (Helianthus annuus L.), wild type (wt), Rubisco-deficient (-RBC), FNR-deficient (-FNR), and Cyt b(6)f deficient (-CBF) transgenic tobacco (Nicotiana tabacum L.) were grown in a growth chamber. Rubisco protein was measured with quantitative SDS-PAGE and FNR protein content with quantitative immunoblotting. The Cyt b(6)f level was measured in planta by maximum electron transport rate and the photosystem I (PSI) content was assessed by titration with far-red light. The CO(2) response of Rubisco was measured in planta with a fast-response gas exchange system at maximum ribulose 1,5-bisphosphate concentration. Reaction site k(cat) was calculated from V(m) and Rubisco content. Biological variation of k(cat) was significant, ranging from 1.5 to 4 s(-1) in wt, but was >6 s(-1) at 23 degrees C in -RBC leaves. The lowest k(cat) of 0.5 s(-1) was measured in -FNR and -CBF plants containing sufficient Rubisco but having slow electron transport rates. Plotting k(cat) against PSI per Rubisco site resulted in a hyperbolic relationship where wt plants are on the initial slope. A model is suggested in which Rubisco Activase is converted into an active ATP-form on thylakoid membranes with the help of a factor related to electron transport. The activation of Rubisco is accompanied by the conversion of the ATP-form into an inactive ADP-form. The ATP and ADP forms of Activase shuttle between thylakoid membranes and stromally-located Rubisco. In normal wt plants the electron transport-related activation of Activase is rate-limiting, maintaining 50-70% Rubisco sites in the inactive state.
authors: Department of Plant Physiology and Biophysics, Institute of Molecular and Cell Biology, University of Tartu, Riia 23, Tartu 51010, Estonia.
authors: H
authors: H
authors: Eichelmann
authors: E
authors: E
authors: Talts
authors: V
authors: V
authors: Oja
authors: E
authors: E
authors: Padu
authors: A
authors: A
authors: Laisk
mesh_terms: D004579:Electron Transport; D007700:Kinetics; D010788:Photosynthesis; D010940:Plant Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D010944:Plants / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D012273:Ribulose-Bisphosphate Carboxylase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D010940:Plant Proteins; D012273:Ribulose-Bisphosphate Carboxylase