SUMMARY: Accumulation of label from a suspension (pH 4·0) of containing 100 m-glucose and 1 m-[S]sulphite was initially rapid. Net accumulation ceased after 5 min, but at this time [S]sulphite was still transported by organisms, and could be washed out to an extent that depended on the wash volume. Pre-incubation in the absence of glucose, and omitting glucose from the reaction mixture, had no effect on initial velocity of sulphite accumulation, although it decreased the total amount accumulated. Initial velocity of accumulation was also unchanged when organisms were pre-incubated in the presence of 2-deoxy--glucose and this inhibitor was included in the reaction mixture. Initial velocity of sulphite accumulation decreased logarithmically as the pH value of the suspension was increased from 3·0 to 5·0; the decrease closely paralleled the decline in concentration of molecular SO over this pH range. Woolf–Hofstee plots for accumulation of SO, at pH 3·0 or 4·0, gave near-vertical plots. Raising the temperature from 19 to 39°C increased the initial velocity of SO accumulation. The initial velocity of transport was not affected by pretreatment of organisms with carbonyl cyanide -chlorophenylhydrazone, DNP or iodoacetamide but pretreatment with 20 m-uranyl nitrate increased the initial velocity almost threefold. It is concluded that SO is transported into by simple diffusion.


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