SUMMARY: Thiamin caused depression of growth, a marked decrease in cellular vitamin B content and cytochrome oxidase activity in yeasts growing in a vitamin B-free medium under aerobic conditions but had practically no effect in and spp. Pyridoxine added concomitantly with thiamin permitted the thiaminsensitive yeasts to grow normally with increased activity of cytochrome oxidase. δ-Aminolaevulinate also caused the increase in cytochrome oxidase activity but growth was only partially improved by the addition of this precursor of haem biosynthesis. These phenomena were similar to those found previously in strain 4228 (ATCC 9080) (Nakamura , 1981). Thiamin-sensitive yeasts accumulated thiamin more than 24-fold when compared with the thiamin-insensitive cells. Thiamin transported into the thiamin-sensitive yeasts was recovered only in the non-esterified form. Thiamin added to the growth medium was also accumulated by growing cells of the thiamin-sensitive yeasts especially during the lag and early exponential phases of growth. Pyridoxine did not affect either thiamin accumulation or the intracellular form of the transported thiamin.


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