Thioredoxin-mediated reduction of photosynthetic carbon reduction enzymes following chilling in the light
Hutchison, Ronald Scott
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https://hdl.handle.net/2142/20615
Description
Title
Thioredoxin-mediated reduction of photosynthetic carbon reduction enzymes following chilling in the light
Author(s)
Hutchison, Ronald Scott
Issue Date
1994
Doctoral Committee Chair(s)
Ort, Donald R.
Department of Study
Plant Biology
Discipline
Plant Biology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Botany
Chemistry, Biochemistry
Language
eng
Abstract
Exposure of tomato plants (Lycopersicon esculentum) to low temperatures and high irradiance results in a marked inhibition in photosynthesis. This inhibition is centered on the enzymes of the photosynthetic carbon reduction cycle (PCRC). The enzyme fructose-1,6-bisphosphatase (FBPase) was isolated and characterized from both plants illuminated at low temperature as well as control plants. Isolated FBPase from both plants was effectively reduced by thioredoxin. The chilling treatment had no effect on the midpoint potential of the regulatory sulfhydryl groups ($-$310 mV), indicating no direct chilling damage to the enzyme. Thiol labeling of FBPase in vivo showed that there was a 60% decrease in sulfhydryl labeling following chilling, indicating that a lower level of reduction of FBPase following chilling was responsible for the inhibition of photosynthesis. In order to better understand the process of reductive activation, thioredoxin f, phosphoribulokinase, sedoheptulose-1,7-bisphosphatase from the PCRC were purified. The midpoint potentials of thioredoxin f and phosphoribulokinase were around $-$270 mV, while sedoheptulose-1,7-bisphosphatase had a potential of $-$310 mV. The enzymes with the lowest (i.e. most negative) midpoint potential are the ones that show the largest decline in activity following chilling. The difference in midpoint potentials also suggests that the ferredoxin-thioredoxin system may act as a modulator of enzyme activity for the low potential enzymes rather than just an off/on switch as appears to be the case for phosphoribulokinase.
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