COMPLEX-FORMING PROPERTIES OF BUTANEDIONE-MODIFIED FERREDOXIN-NADP+ REDUCTASE WITH NADP+ AND FERREDOXIN

The plastidic ferredoxin-NADP+ reductase from the xanthophycean alga Bumilleriopsis [filiformis] forms a stoichiometric 1:1 complex with ferredoxin and NADP+ which is demonstrated by difference spectra of both complexes. Butanedione modification of the flavoprotein results in loss of its enzymatic activities (transhydrogenase and diaphorase) concurrently with its capability to form a complex with NADP+, whereas the ferredoxin-binding site is scarcely influenced by the modifying reagent and complex formation is still possible. Apparently butanedione specifically reacts with the arginine residue of the protein involved in binding of pyridine nucleotides at the active site. The previous proposal of different binding sites for ferredoxin and pyridine nucleotides at the reductase was supported.