Uptake and Metabolism of Sulfate by Chlorella. I. Sulfate Accumulation and Active Sulfate

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Abstract
The uptake and active accumulation of sulfate by C. pyrenoidosa has been studied with the aid of S35O4 = in combination with chromatography and ionophoresis of materials extracted from the cells. The accumulation of sulfate by Chlorella in the form of sulfate determined by chromatography of cell extracts is metabolic in nature and results in higher concentrations of SO4= recoverable from the cells than exist in the external solution. Provision of light during the uptake period enhances the accumulation of sulfate by Chlorella, and simultaneous treatment with 2,4-dinitrophenol during uptake of sulfate causes a reduction in both SO4= and total S in the cell. The effect of 2,4-dinitrophenol is greater in cells provided with exogenous sucrose taking up sulfate in darkness than in normal cells given illumination during uptake. Perchloric acid extraction at low temperatures and adsorption of nucleotide sulfate compounds on charcoal makes possible separation of 2 and perhaps 3 compounds which contain radioactive S and also absorb ultraviolet light. Quantitative determinations of these compounds show that as much as 10% of the total S taken up by Chlorella in a 1-hour exposure to sulfate can be accounted for in these materials. Light is less important for the formation of nucleotide sulfate compounds than for total uptake of sulfate and the effect of 2,4-dinitrophenol on incorporation of labeled sulfate into these compounds in both light and darkness is relatively the same. These differences indicate that it is unlikely that these compounds are responsible for sulfate accumulation by Chlorella.