Analysis of a ferric leghemoglobin reductase from cowpea (Vigna unguiculata) root nodules.

Ferric leghemoglobin reductase (FLbR), an enzyme reducing ferric leghemoglobin (Lb) to ferrous Lb, was purified from cowpea (Vigna unguiculata) root nodules by sequential chromatography on hydroxylapatite followed by Mono-Q HR5/5 FPLC and Sephacryl S-200 gel filtration. The purified cowpea FLbR had a specific activity of 216 nmol Lb(2+)O(2) formed min(-1) mg(-1) of enzyme for cowpea Lb(3+) and a specific activity of 184 nmol Lb(2+)O(2) formed min(-1) mg(-1) of enzyme for soybean Lb(3+). A cDNA clone of cowpea FLbR was obtained by screening a cowpea root nodule cDNA library. The nucleotide sequence of cowpea FLbR cDNA exhibited about 88% similarity with soybean (Glycine max) FLbR and 85% with pea (Pisum sativum) dihydrolipoamide dehydrogenase (DLDH, EC 1.8.1.4) cDNAs. Conserved regions for the FAD-binding site, NAD(P)H-binding site, and disulfide active site were identified among the deduced amino acid sequences of cowpea FLbR, soybean FLbR, pea DLDH and other enzymes in the family of the pyridine nucleotide-disulfide oxido-reductases.