Nine strains of yeasts in intact cells were investigated with respect to the oxidation of exogenously supplied substrates : glucose, arabinose, ethanol, pyruvate, gluconate and the TCA cycle intermediates and the effects of monoiodoacetic acid, sodium fluoride and arsenite on oxygen uptake and carbon dioxide output.
1. In general, yeasts which have comparatively low RQ values oxidized these above named exogenously supplied substrates more actively than the yeasts with comparatively high RQ.
2. The sensitivity to monoiodoacetic acid varies with the kind of yeast. The inhibition was small on Rhodotorula glutinis and Candida utilis which have comparatively low RQ values and scarcely ferment. Severe inhibition was observed on genera Saccharomyces which actively ferment alcohol. The highest inhibition, however, appeared on Mycoderma cerevisiae which has comparatively high RQ values and on Torula candida which has comparatively low RQ values.
3. Relatively high concentrations of sodium fluoride were needed to inhibit the respiration of yeast. The inhibition was less on Rhodotorula glutinis which has comparatively low RQ values. contrary to this, Saccharomyces cerevispae which has comparatively high RQ values is remarkably inhibited.
4. Similar effect was observed as a result of the addition of arsenite to yeasts. Rhodotorula glutinis was insignificantly inhibited. Saccharomyces sake which has comparatively high RQ values was greatly inhibited.
5. The results obtained by means of microspectroscopic study showed some variations of absorption bands of cytochromes. However, by the study using a spectrophotometer, it is found that there are no great differences among cytochrome components of yeast tested.
6. The variations in permeability of the intact cells and the decrease of enzyme activities may cause the differences in oxidation rate of exogenously supplied substrates and in sensibility against inhibitors.
7. The ability in respect to oxidation of ethanol in Rhodotorula glutinis was adaptively acquired by preincubation in either ethanol, acetaldehyde or acetate.