Amino acid sequences of ferredoxin isoproteins from radish roots

Three ferredoxin isoproteins (R-Fd A, R-Fd B-1, and R-Fd B-2) were purified from white roots of radish (Raphanus sativus L. var. acantiformis cultivar Miyashige) and two isoproteins (L-Fd A and L-Fd B) from leaves. The amino acid sequences of three of them (L-Fd A, R-Fd B-1, and R-Fd B-2) were determined and compared with one another and with those of other higher plant ferredoxins so far studied. L-Fd A and R-Fd B-1 had heterogeneities at four and two amino acid sites, respectively. Two isoprotein (R-Fd B-1 and R-Fd B-2) were deduced to be expressed only in root tissue on the basis of sequence studies and amino acid compositions of all isoferredoxins isolated from the radish plant. The root ferredoxins sequenced in this study were similar to each other, but quite different from other higher plant ferredoxins, all of which were isolated from leaf tissue. The coupling activities of these ferredoxin isoproteins were measured in the NADP+-photoreduction system of radish chloroplasts and glutamate synthase [EC 1.4.7.1] systems isolated from radish leaf and root tissues. No distinctive physiological characteristics were observed among these isoferredoxins.