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Ferredoxin-NADP+ reductase from the microalga Bumilleriopsis was isolated by a combination of affinity chromatography on a flavodoxin-Sepharose 4 B column and usual purification procedures. Both the elution pattern of the final gel filtration step and of the sodium dodecylsulfate (SDS) disc gel electrophoresis indicate that there are at least two different molecular-weight forms of the reductase, a monomeric form and a dimeric one.

Data regarding the role of oxygen in nitrite reduction are presented. In an NADPH-generating system including homogeneously purified ferredoxin-NADP reductase, ferredoxin (or flavodoxin) and nitrite reductase from the alga Bumilleriopsis filiformis, oxygen and nitrite can be reduced simultaneously. In air, rates of 1.2 mumol nitrite reduced-min-1-mg-1 nitrite reductase are obtained, which are physiologically feasible. Ferredoxin is inhibited non-competitively by oxygen during nitrite reduction. Oxygen uptake due to the oxidase reaction of ferredoxin-NADP reductase mediated by flavodoxin from Chlorella fusca and ferredoxin from Bumilleriopsis involves superoxide and is inhibited by the nitrite reducing system.