The NADP+‐binding site of ferredoxin‐NADP+ reductase

Abstract

The [spinach] flavoprotein ferredoxin-NADP reductase is inactivated and loses its ability to bind NADP during covalent modification of a lysine by 5-dimethylaminonaphthalene-1-sulfonyl chloride (dansyl chloride). The substrate NADP gives almost complete protection against inactivation and modification. These observations are extended in this report by the characterization of an octapeptide containing the dansyl-lysine which was isolated by high-performance liquid chromatography from tryptic digests of protein modified with radiolabeled reagent. The amount of this peptide was severely reduced in protein modified in the presence of NADP. The sequence of the dansyl-peptide, only partially obtained by Edman degradation, was completed by analysis of the fragments resulting from thermolysin digestion of the purified tryptic dansyl-peptide. Thus, the octapeptide containing the essential lysine residue has the following sequence: H2N-Ser-Val-Ser-Leu-Cys-Val-Lys-Arg-COOH. A comparison with coresponding sequences of other known NADP-dependent dehydrogenases is attempted.