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Articles

Studies of Sulfate Utilization by Algae

9. Fractionation of a Cell-free System from Chlorella into Two Activities Necessary for the Reduction of Adenosine 3'-Phosphate 5'-Phosphosulfate to Acid-Volatile Radioactivity ¹

^a Department of Biology, Brandeis University, Waltham, Massachusetts 02154

Further properties of the enzymatic system obtained from Chlorella pyrenoidosa (Emerson strain 3) which reduces adenosine 3'-phosphate 5'-phosphosulfate-³⁵S to acid-volatile radioactivity, when fortified with Mg²⁺ and 2, 3-dimercaptopropan-1-ol as reductant, are described. Optimal concentrations of adenosine 3'-phosphate 5'-phosphosulfate-³⁵S and Mg²⁺ and the pH optimum have been determined. 2,3-Dimercaptopropan-1-ol can be replaced by dithiothreitol, mercaptoethanol, reduced glutathione, cysteine, and cysteamine. Treatment of the crude extracts with ammonium sulfate and alumina C-gamma gel yields two fractions, designated "S" and "A," which must be recombined to obtain acid-volatile radioactivity. Further fractionation of fraction S by ammonium sulfate gradient elution and diethylaminoethyl cellulose chromatography yields approximately a 50-fold increase in specific activity compared to that found in the crude extract. This material appears to contain an active component with a molecular weight estimated by agarose gel chromatography of about 330,000.

¹ Supported by Grant GB 4231 from the National Science Foundation.

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