[Role of the pterin component in light and dark oxygen consumption by chloroplasts]

The effects of ferredoxin and the pterin component from pea chloroplasts on oxygen consumption by pea and spinach chloroplasts in the dark and in the light were studied. In the absence of the pterin component the illuminated chloroplasts from both sources weakly reduce oxygen. An addition of the pterin component produces different effects on oxygen consumption by pea and spinach chloroplasts: the former efficiently reduce oxygen after addition of a single pterin component, while the latter require the presence of ferredoxin as well. The data obtained suggest that in pea chloroplasts there exists a ferredoxin-independent pseudocyclic electron transport mediated by pterin. In spinach chloroplasts this electron transport is ferredoxin-dependent. In the presence of pterins the chloroplasts are capable of carrying out dark reduction of O2, using NADPH and H+ as electron donors.