. Biochemistry of plants and animals, an introduction. Biochemistry. 334 ANIMAL BIOCHEMISTRY Function Riboflavin serves by way of one of the above prosthetic groups as a hydrogen-electron carrier, as mentioned earlier. The isoalloxazine portion of the molecule is subject to reversible oxidation and reduc- tion according to the reaction shown, R CH; + AH2. O where AH2 represents a suitable reducing agent and R the rest of the structure for either FMN or FAD. The R group helps contribute a physiologically suitable oxidation-reduction potential and provides for attachment to the apoenzyme compone
. Biochemistry of plants and animals, an introduction. Biochemistry. 334 ANIMAL BIOCHEMISTRY Function Riboflavin serves by way of one of the above prosthetic groups as a hydrogen-electron carrier, as mentioned earlier. The isoalloxazine portion of the molecule is subject to reversible oxidation and reduc- tion according to the reaction shown, R CH; + AH2. O where AH2 represents a suitable reducing agent and R the rest of the structure for either FMN or FAD. The R group helps contribute a physiologically suitable oxidation-reduction potential and provides for attachment to the apoenzyme component. It is now known that the various flavoproteins are also metallo- protcins containing either Mo+ + , Cu++, or Fe+ + . These ions are important to the activity of the enzymes since their removal blocks the ordinary function. Probably the prosthetic group accepts the electrons and transfers them to the metal ion, which in turn transfers electrons to the next component of the chain. 2H3O+ + (2^) + FAD • Fe2+++ protein -^ ;0 + FADHo • Fe2+++ protein i FAD • Fe2+++ protein + {2e) <- FAD • Feo++ protein + 2H3O+ In this system the electrons come in one end from a reduced substrate and are accepted at the other by an oxidized substrate. It is believed that in at least one flavoprotein there are four iron ions for each FAD instead of the two written here for the sake of convenience. The particular electron-transfer system outlined on page 172 in- volves the flavoprotein called cytochrome reductase and functions by the above mechanism. DPNH supplies the electrons to the cytochrome reductase, which transfers them to cytochrome on the way to mo- lecular oxygen. Although this pathway may not represent the only one in animals, it is certainly the major one. Hence, the importance of riboflavin in the diet becomes evident for all those animals unable to synthesize il. In addition to cytochrome reductase, there are other important flavoenzymes. Xanthine oxidase, for example,
Size: 2215px × 1128px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookpublishernewyorkwiley, booksubjectbiochemis
