Oxidation-reduction properties of thioredoxins and thioredoxin-regulated enzymes

Oxidation-reduction midpoint potentials have been measured for the two chlo roplast thioredoxins, thioredoxin f and m, for ferredoxin:thioredoxin reduc tase (FTR) and for the thioredoxin-regulated enzymes fructose-1,6-bisphosph atase (FBPase), phosphoribulokinase and NADP-malate dehydrogenase. The effe cts of pH on the midpoint potentials of these chloroplast proteins have bee n measured so that the effect of the light-induced increase in chloroplast stromal pH on the redox properties of the proteins can be calculated. Spect roscopic measurements on FTR and on an N-ethylmaleimide-modified derivative of the enzyme have been used to elucidate the role of the [4Fe-4S] cluster of FTR during the reduction of the enzyme's active-site disulfide by ferre doxin.