Purification and Characterization of Flavodoxin from Peptostreptococcus elsdenii

Abstract

Abstract Flavodoxin has been crystallized from Peptostreptococcus elsdenii grown at low iron concentrations. The properties of this protein are similar to those of flavodoxin from Clostridium pasteurianum. It has a molecular weight of about 15,000 and contains 1 molecule of flavin mononucleotide per molecule of protein. It does not contain labile sulfide or iron. It lacks the amino acid histidine. Ferredoxin and flavodoxin are interchangeable in the oxidation of pyruvate by extracts of P. elsdenii from media either high or low in iron, and in the phosphoroclastic reaction of C. pasteurianum. On a molar basis flavodoxin is somewhat less effective than ferredoxin in these systems. Flavodoxin is reduced by light irradiation in the presence of EDTA and an intermediate having a spectrum characteristic of flavin neutral semiquinone is generated. The rate and extent of reduction are pH-dependent. The spectrum of the semiquinone is unaffected at high pH and by high concentrations of urea. The extinction coefficient of oxidized flavodoxin at 445 mµ is 10,200 m-1 cm-1. The extinction coefficient of flavodoxin semiquinone at 580 mµ is 4,500 m-1 cm-1.