Regulation of chloroplast enzyme activities by thioredoxins: activation orrelief from inhibition?

Studies on redox signaling and light regulation of chloroplast enzymes have highlighted the importance of the ferredoxin-thioredoxin thiol-disulfide i nterchange cascade. Recent research has focused on the intramolecular mecha nism by which the reduction status of a chloroplast enzyme affects its cata lytic properties, and site-directed mutagenesis has been used to identify t he regulatory cysteines involved. For some of the thiol-regulated enzymes, structure-function studies have revealed that the complex conformational ch anges 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.