The Interaction of Ferredoxin with Chloroplast Ferredoxin-Linked Enzymes

Abstract

Ferredoxin, reduced by Photosystem I during oxygenic photosynthesis, then serves as the electron donor for the reduction of NADP+ [1], nitrite [2], and the reductive conversion of 2-oxoglutarate plus glutamine to glutamate [3]. Evidence exists thit two of these ferredoxin-dependent reductions, that of NADP+ (catalyzed by ferredoxin:NADP+ oxidoreductase, hereafter abbreviated FNR) and of nitrite to ammonia (catalyzed by ferredoxinmitrite oxidoreductase, hereafter referred to as nitrite reductase) involve electrostatically-stabilized complexes between ferredoxin and the enzymes [4,5]. Glutamate synthase, the enzyme responsible for the ferredoxin-dependent synthesis of glutamate, like FNR [6] and nitrite reductase [7], can be purified by ferredoxin affinity chromatography [8]. This suggested that glutamate synthase can form an electrostatic complex with ferredoxin. Evidence for such a complex [9] is presented below.