Regulation by Redox Poise in Chloroplasts

摘要

The protein thioredoxin controls the re-dox state of regulatory sulfhydryl-disulfide bonds in many eukaryotic and prokaryotic enzymes. Indeed, light exerts its regulatory effect on photosynthesis through the action of reduced thioredoxin. Reduction ofregulatory sulfhydryl-disulfide systems by reduced thioredoxins in the chloroplast stroma accelerates several key enzymes of the reductive pentose phosphate pathway, as well as the adenosine 5'-triphosphate (ATP)-synthase complex. The reduction of thioredoxin is linked directly to the functioning of the photosynthetic electron transfer chain through the electron transfer protein ferredoxin (Fd). As Fd becomes reduced by photosystem I (PS I) in the light, it poises the reduction state of the chloroplast chioredoxins by reducing ferre-doxin-thioredoxin reductase, which in turn reduces the thioredoxins. This elegant system is now shown to regulate more than the enzymes of photosynthesis.