Non-enzymatic Reduction of Sennidins and Sennosides by Reduced Flavin

抄録

Reduced flavin-adenine dinucleotide (FADH₂), which was produced by flavin-adenine dinucleotide (FAD) -dependent sennidin reductase, reduced methyl orange non-enzymatically in a molar ratio of 2 : 1 under anaerobic conditions. Similarly, sennidins and sennosides were reduced nonenzymatically to rheinanthrone and 8-glucosylrheinanthrone, respectively, by the reduced forms of cofactors such as FAD, flavin mononucleotide (FMN), riboflavin and benzyl viologen. The reaction was inhibited by oxygen. FADH₂ reduced sennidins equimolarly, but sennosides were reduced much less effectively than sennidins (about one-tenth).
The polarographic half-wave potentials of sennidins A and B, and sennosides A and B were-115, -133, -184and-201mV, respectively.
Therefore, it was confirmed that the reduction of sennidins and sennosides by FAD-dependent sennidin reductase consists of the following two reactions; (1) the reductase reduces cofactors such as FAD and (2) sennidins and sennosides are reduced non-enzymatically by the reduced forms of cofactors.
On the other hand, oxidation of rheinanthrone to sennidins in a neutral solution occurred with oxygen but not with FAD.