Reiko Ando

A flavoenzyme model: Facile oxidation of thiols by a flavin immobilized in cationic polyelectrolytes☆

Abstract The reactions of a polymer-bound flavin with thiols (2-mercaptoethanol, glutathione, thiophenol, and 1,4-butanedithiol) are remarkably accelerated, when compared with that of a monomeric flavin. The rate enhancements observed were 30- to 6000-fold. In particular, thiophenol which had been believed not to be oxidized by flavin in nonenzymatic systems was oxidized most rapidly among the monothiols examined. The reaction rates were improved by incorporation of a dodecyl group into the flavin-containing polymer. Therefore, the hydrophobic nature of the cationic polymer matrix was concluded to be responsible for the large rate enhancement among other factors.

Controlled organization of cyanine and merocyanine dyes at the surface of synthetic bilayer membranes

Some water-soluble cyanine and merocyanine dyes bound to a synthetic bilayer membrane show drastic spectral changes which are sensitive to the phase transition and the chemical structure of the membrane.

Catalyses by polymer complexes. Part 3. Polymer micellar catalysis of isoalloxazine (flavin) oxidation of thiols

The effect of cationic polymer micelles on the isoalloxazine (flavin) oxidation of thiols is reported: the polymers employed were poly-(2-ethyl-1-vinylimidazole) quaternized with ethyl bromide and lauryl bromide [lauryl group content: 8.8 mol %(L-9), 28.9 mol %(L-29), and 40.9 mol %(L-41)]. Addition of L-29 and L-41 polymers caused a red shift of the u.v. absorption maximum of thiophenoxide ion and an increase in its acid dissociation constant, while L-9 polymer scarcely affected these values. Under anaerobic conditions, the oxidation of thiophenol and 2-mercaptoethanol by 10-ethyl-3-methylisoalloxazine in the presence of micelle-like polymers (L-29 and L-41) was 102–105 times faster than the corresponding reaction in a non-polymeric system, whereas L-9, a polyelectrolyte-like polymer, produced almost no acceleration. The thiolate anion bound to the polymer domain is activated probably due to the formation of a hydrophobic ion pair. On the other hand, the oxidation of butane-1,4-dithiol was not much affected by the polymer micelle. The difference in mechanism of dithiol oxidation is discussed in connection with the microenvironmental effect.