Regulation of Nitrite Reductase in the Cyanobacterium Anacystis nidulans

Abstract

Summary: The effect of the nitrogen source on the activity of ferredoxin-dependent nitrite reductase has been studied in the cyanobacterium Anacystis nidulans. De novo synthesis of nitrite reductase occurred in the absence of an added nitrogen source, although enzyme activity was higher when the medium contained either NO3 − or NO2 −. The positive effect of NO3 − on nitrite reductase was also evident in tungstate-treated A. nidulans, which lacked an active nitrate reductase, indicating that the stimulatory effect was due to NO3 − itself and not to the NO2 − resulting from its intracellular reduction. NH4 + acted as a repressor, overriding any positive effect of NO3 − or NO2 −. Nitrite reductase synthesis was freed from NH4 + repression by l-methionine-DL-sulphoximine, an irreversible inhibitor of glutamine synthetase. NH4 + must therefore be metabolized through glutamine synthetase before repressing nitrite reductase. The kinetics of nitrate reductase and nitrite reductase development were similar in cells transferred from NH4 +- to NO3 −-containing media, suggesting a coordinate regulation of synthesis.