Abstract
Dark-operative protochrolophyllide reductase (DPOR) is a nitrogenase-like enzyme consisting of three subunits, ChlL, ChlN and ChlB, and plays a critical role in chlorophyll biosynthesis in the dark. DPOR is distributed widely not only in anoxygenic photosynthetic bacteria but also in oxygenic phototrophs, which raises a question how the nitrogenase-like DPOR operates in oxygenic photosynthetic cells. Here we report functional expression of cyanobacterial DPOR compornents in the cyanobacterium Leptolyngbya boryana to examine the oxygen sensitivity. We constructed plasmids for overexpression of ChlL and ChlN-ChlB. We detected unambiguous DPOR activity by mixing two crude extracts of L. boryana overexpressing ChlL and ChlN-ChlB, allowing to evaluating the activities of L-protein and NB-protein individually. L-protein activity in the extract was almost lost upon the exposure to oxygen for 10 min, while NB-protein activity was maintained after 60 min exposure. These results suggest that L-protein is the target of oxygen inactivation in cyanobacterial cells.
