The enzyme contains a [4Fe-4S] cluster and internal disulfide. It forms a mixed disulfide with thioredoxin on one side, and docks ferredoxin on the other side, enabling two one-electron transfers. The reduced thioredoxins generated by the enzyme activate the Calvin cycle enzymes EC 3.1.3.11 (fructose-1,6-bisphosphatase), EC 3.1.3.37 (sedoheptulose-bisphosphatase) and EC 2.7.1.19 (phosphoribulokinase) as well as other chloroplast enzymes by disulfide reduction.