PMID: 166990Jan 10, 1975

Reduced diphosphopyridine nucleotide peroxidase. Intermediates formed on reduction of the enzyme with dithionite or reduced diphosphopyridine nucleotide

The Journal of Biological Chemistry
M I Dolin


DPNH peroxidase is a flavin adenine dinucleotide-containing flavoprotein. Anaerobic titration of enzyme with dithionite has shown that the active site of the enzyme contains 2 mol of flavin and in addition 1 mol of a non-flavin electron acceptor that is tentatively identified as a disulfide group. Thus complete reduction of the enzyme requires 3 mol of dithionite per mole of active site. The first mole of dithionite reduces the non-flavin acceptor; complex formation between the reduced acceptor and one of the bound flavin molecules causes the formation of a long wavelength absorption band between 500 and 670 nm. The second mole of dithionite reduces the flavin that interacts with the reduced non-flavin group, and the long wavelength band disappears. The third mole of dithionite reduces the second mole of flavin. All groups are reoxidized in the presence of air. DPNH reacts with only two of the enzyme-bound electron acceptors. The first mole of DPNH reduces the non-flavin group to form an intermediate (I) that is almost identical with that formed by dithionite. The second mole of DPNH complexes with the second flavin of Intermediate I to form Intermediate II. This reaction causes a further absorbance increase in the long wavelen...Continue Reading

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