Article: Proceedings of the National Academy of Sciences

Dark deactivation of chloroplast enzymes finally comes to light. JP Jacquot. P.Ā Proceedings of the National Academy of Sciences

From the pioneering work that the Buchanan group started in the late 1960s, we know that the division of photosynthesis into light and dark reactions is inade- quate because the activity of a number of chloroplast enzymes, many involved in the Calvinā€“Benson cycle, is strictly controlled by light; that is, they are activated in the light and deactivated in the dark. An exception is glucose-6-phosphate dehydrogenase, which is regulated in an opposite manner; that is, activation in the dark and deactivation in the light. It took a decade to biochemically dissect the newly identifed redox regula- tory pathway responsible for this regulation. Known as the ferredoxin-thioredoxin system, the pathway is com- posed of three components: ferredoxin, ferredoxin- thioredoxin reductase (FTR), and thioredoxin (Trx) that relay the reducing power generated at photosystem 1 (PS1) to target regulatory enzymes (1, 2).