Regulation of NADP-Malate Dehydrogenase Light-Activation by the Reducing Power. I Functional Studies
NADP-malate dehydrogenase (MDH) light — activation via the ferredoxin-thioredoxin system requires a low light energy for saturation (1). Nevertheless, high light pretreatments which affect the functionning of photosystem II reaction centers were reported to inhibit enzyme light-activation in crude leaf extracts and in isolated chloroplasts (2,3). In the present work, we investigated the effect of photoinhibitory pretreatments on the different steps of the thiol-disulfide interchange cascade leading to MDH light-activation, in order to establish the relationship between the reduction state of the proteins of the system and the extent of activation of the target enzyme. For that purpose, a model system has been used, composed of isolated thylakoids and all the purified proteins of the ferredoxin-thioredoxin system at optimized concentrations.
KeywordsReduction State Disulfide Bridge Probability Curve Reconstituted System Crude Leaf Extract
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