Regulation of chloroplast enzyme activities by thioredoxins: activation or relief from inhibition?
Studies on redox signaling and light regulation of chloroplast enzymes have highlighted the importance of the ferredoxin-thioredoxin thiol-disulfide interchange cascade. Recent research has focused on the intramolecular mechanism by which the reduction status of a chloroplast enzyme affects its catalytic properties, and site-directed mutagenesis has been used to identify the regulatory cysteines involved. For some of the thiol-regulated enzymes, structure-function studies have revealed that the complex conformational changes that occur might be associated with disulfide isomerization and auto-inhibition. Transgenic approaches indicate that this regulation constitutes a rapid means to adjust enzyme activity to metabolic needs.