caa a22 4500 445890169 CHVBK 20180317145613.0 cr unu---uuuuu 170323e20110901xx s 000 0 eng 10.1007/s11120-011-9667-8 doi (NATIONALLICENCE)springer-10.1007/s11120-011-9667-8 The activity of Rubisco's molecular chaperone, Rubisco activase, in leaf extracts [Elektronische Daten] [A. Carmo-Silva, Michael Salvucci] Rubisco frequently undergoes unproductive interactions with its sugar-phosphate substrate that stabilize active sites in an inactive conformation. Restoring catalytic competence to these sites requires the "molecular chiropractic” activity of Rubisco activase (activase). To make the study of activase more routine and physiologically relevant, an assay was devised for measuring activase activity in leaf extracts based on the ATP-dependent activation of inactive Rubisco. Control experiments with an Arabidopsis activase-deficient mutant confirmed that the rate of Rubisco activation was dependent on the concentration of activase in the extracts. Activase catalyzed Rubisco activation at rates equivalent to 9-14% catalytic sites per min in desalted extracts of Arabidopsis, camelina, tobacco, cotton, and wheat. Faster rates were observed in a transgenic line of Arabidopsis that expresses only the β-isoform of activase, whereas no activity was detected in a line that expresses only the α-isoform. Activase activity was also low or undetectable in rice, maize, and Chlamydomonas, revealing differences in the stability of the enzyme in different species. These differences are discussed in terms of the ability of activase subunits to remain associated or to reassociate into active oligomers when the stromal milieu is diluted by extraction. Finally, the temperature response of activase activity in leaf extracts differed for Arabidopsis, camelina, tobacco, and cotton, corresponding to the respective temperature responses of photosynthesis for each species. These results confirmed the exceptional thermal lability of activase at physiological ratios of activase to Rubisco. Springer Science+Business Media B.V. (outside the USA), 2011 Rubisco nationallicence Molecular chaperone nationallicence Heat stress nationallicence CO2 assimilation nationallicence AAA+protein nationallicence Photosynthesis nationallicence AAA+ : ATPase associated with diverse cellular activities nationallicence E : Rubisco in the uncarbamylated form nationallicence ECM : Rubisco carbamylated and containing bound Mg2+, E-CO2-Mg2+ nationallicence ER : Rubisco uncarbamylated and containing bound RuBP, E-RuBP nationallicence PEG : Polyethylene glycol nationallicence PPFD : Photosynthetic photon flux density nationallicence Rubisco : Ribulose-1,5-bisphosphate carboxylase/oxygenase nationallicence RuBP : Ribulose-1,5-bisphosphate nationallicence T 0.5 : Temperature that inhibits activity by 50% nationallicence Carmo-Silva A. U.S. Department of Agriculture, Agricultural Research Service, Arid-Land Agricultural Research Center, 21881N Cardon Lane, 85138, Maricopa, AZ, USA aut Salvucci Michael U.S. Department of Agriculture, Agricultural Research Service, Arid-Land Agricultural Research Center, 21881N Cardon Lane, 85138, Maricopa, AZ, USA aut Photosynthesis Research Springer Netherlands 108/2-3(2011-09-01), 143-155 0166-8595 108:2-3<143 2011 108 11120 https://doi.org/10.1007/s11120-011-9667-8 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/s11120-011-9667-8 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Carmo-Silva A. U.S. Department of Agriculture, Agricultural Research Service, Arid-Land Agricultural Research Center, 21881N Cardon Lane, 85138, Maricopa, AZ, USA aut NATIONALLICENCE 700 1- Salvucci Michael U.S. Department of Agriculture, Agricultural Research Service, Arid-Land Agricultural Research Center, 21881N Cardon Lane, 85138, Maricopa, AZ, USA aut NATIONALLICENCE 773 0- Photosynthesis Research Springer Netherlands 108/2-3(2011-09-01), 143-155 0166-8595 108:2-3<143 2011 108 11120 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer