Abstract
Biochemical investigations of the properties of free flavins and of flavoproteins have shown that reduction usually occurs in two stages, with the intermediate formation of semiquinones in the case of free flavins. Flavoproteins often show spectroscopically similar intermediates, when partially reduced with substrate. These may, however, be enzyme-product complexes. Detailed investigation of individual flavoprotein enzymes has shown examples in which catalysis involves transition of the enzyme between oxidized and fully reduced forms (glucose oxidase), between oxidized and intermediate forms (D-amino acid oxidase), and intermediate and fully reduced forms (TPNH—cytochrome c reductase). Further, examples are known in which both intermediate and reduced forms react with oxygen, in which only one reacts, while in TPNH—cytochrome c reductase neither the intermediate nor the reduced form reacts with molecular oxygen. The physiological significance of these complex findings is uncertain, partly because it is not known whether purified flavoproteins occur in the same form in the tissues. It seems unlikely, however, that flavoproteins make a major contribution to the respiratory exchange of mammals.
Full Text
The Full Text of this article is available as a PDF (589.9 KB).
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- BEINERT H. Evidence for an intermediate in the oxidation-reduction of flavoproteins. J Biol Chem. 1957 Mar;225(1):465–478. [PubMed] [Google Scholar]
- GIBSON Q. H., HASTINGS J. W. The oxidation of reduced flavin mononucleotide by molecular oxygen. Biochem J. 1962 May;83:368–377. doi: 10.1042/bj0830368. [DOI] [PMC free article] [PubMed] [Google Scholar]
- GIBSON Q. H., MASSEY V., ATHERTON N. M. The nature of compounds present in mixtures of oxidized and reduced flavin mononucleotides. Biochem J. 1962 Nov;85:369–383. doi: 10.1042/bj0850369. [DOI] [PMC free article] [PubMed] [Google Scholar]
- GIBSON Q. H., SWOBODA B. E., MASSEY V. KINETICS AND MECHANISM OF ACTION OF GLUCOSE OXIDASE. J Biol Chem. 1964 Nov;239:3927–3934. [PubMed] [Google Scholar]
- MASSEY V., GIBSON Q. H. ROLE OF SEMIQUINONES IN FLAVOPROTEIN CATALYSIS. Fed Proc. 1964 Jan-Feb;23:18–29. [PubMed] [Google Scholar]
- Straub F. B. Isolation and properties of a flavoprotein from heart muscle tissue. Biochem J. 1939 May;33(5):787–792. doi: 10.1042/bj0330787. [DOI] [PMC free article] [PubMed] [Google Scholar]
- VEEGER C., MASSEY V. Inhibition of lipoyl dehydrogenase by trace metals. Biochim Biophys Acta. 1960 Jan 1;37:181–183. doi: 10.1016/0006-3002(60)90108-6. [DOI] [PubMed] [Google Scholar]