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Title: REGULATION OF RUBISCO ACTIVASE BY THIOREDOXIN-F AND REDOX

Author
item ZHANG, NING - CROP SCIENCE UOFI URBANA
item PORTIS JR, ARCHIE

Submitted to: Plant Physiology Supplement
Publication Type: Abstract Only
Publication Acceptance Date: 7/19/2000
Publication Date: 7/19/2000
Citation: Zhang, N., Portis Jr, A.R. 2000. Regulation of rubisco activase by thioredoxin-f and redox. Plant Physiology Supplement: p. 164

Interpretive Summary:

Technical Abstract: Arabidopsis Rubisco activase was recently shown to be regulated by redox changes in the larger (46kD) isoform mediated by thioredoxin-f. In this study, we conducted additional experiments to characterize the regulation. The Km for ATP hydrolysis of the 46kD isoform was lowered by 4 to 5-fold after reduction. Only 0.3 micromolar thioredoxin-f was required for a half-maximal activity change after a 5 min preincubation. Arabidopsis normally contains about a 1:1 ratio of the two isoforms and we found that a 1:1 ratio of the Arabidopsis isoforms was required for a complete inhibition of the Rubisco activation activity by oxidation and assay at an ATP/ATP ratio of 3:1! Redox titrations give a midpoint potential of -344mV for the 46kD isoform and -342mV for FBPase, consistent with previous reports indicating that Rubisco and FBPase are co-regulated by light intensity. Transgenic plants expressing 46kD isoforms with Cys-Ala substitutions in the carboxyl-terminus unique to this isoform, lost the ability to down-regulate Rubisco activity during a high to low light transition in contrast to plants expressing only the 46kD isoform. We conclude that the presence of a 46kD isoform containing both Cys residues, is required for the light modulation of Rubisco activity in Arabidopsis. These cysteines apparently form a disulfide upon oxidation, which alters nucleotide binding and thereby sensitivity to the ATP/ADP ratio.