Synergistic reduction of toluylene blue induced by acetaldehyde and menadione in yeast cell suspension: Application to determination of yeast cell activity

- Toluylene blue (TB) was synergistically reduced by menadione and acetaldehyde.
- The post-addition of acetaldehyde was essential for synergistic reduction of TB.
- Yeast cell activity was determined by the synergistic reduction of TB within 2 min.
- TB reduction was proportional to yeast cell density from 104 to 2×106 cells/ml.
- TB reduction was applicable to the cytotoxicity test.

Membrane permeant acetaldehyde and menadione induced the synergistic reduction of toluylene blue (TB) acting as non-membrane permeant redox indicator in yeast cell suspension. NADH and acetaldehyde also induced the synergistic TB reduction in permeabilized yeast cells and phosphate buffer, but menadione had no ability to promote TB reduction. The pre-incubation of acetaldehyde inhibited the above synergistic reduction of TB in intact and permeabilized yeast cell suspension. The pre-incubation of acetaldehyde might promote NADH oxidation by alcohol dehydrogenase, because acetaldehyde decreased the intracellular NAD(P)H concentration. The above facts indicate that the synergistic reduction of TB is controlled by the order of addition of menadione and acetaldehyde. The synergistic reduction of TB by menadione and acetaldehyde was proportional to viable yeast cell number from 104 to 2×106 cells/ml, and this assay was applicable to cytotoxicity test. The time required for the above assay was only 2 min.