Studies of Sulfate Utilization by Algae. 7. in vivo Metabolism of Thiosulfate by Chlorella

• Published in: Plant physiology (Bethesda) Vol. 43; no. 4; pp. 570 - 577
• Main Authors: Robert C. Hodson, Schiff, Jerome A., Anthony J. Scarsella
• Format: Journal Article
• Language: English
• Published: United States American Society of Plant Physiologists 01.04.1968
• Subjects: Algae; Amino acids; Atoms; Chemical suspensions; Oxidation; Paper chromatography; Plants; Radioactive decay; Sulfates; Sulfur
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.43.4.570

Chlorella pyrenoidosa Chick (Emerson strain 3) utilizes thiosulfate for growth as effectively as sulfate, and more effectively than a variety of organic sulfur compounds containing sulfur in various oxidation states. Thiosulfates, differentially labeled with 35S in either the SH-- or $\text{SO}_{3}$ -- sulfur moieties, were used to follow the incorporation of thiosulfate-sulfur into constituents of the insoluble fraction and of the soluble pools. Labeled sulfate was also used for purposes of comparison. Label from both sulfur atoms of thiosulfate and from sulfate is incorporated into the cysteine, homocysteine, and glutathione of the soluble pools, and into the methionine and cystine of protein in the insoluble fraction. Label from $\text{SO}_{3}$-sulfur of thiosulfate is incorporated more slowly into protein methionine and cystine than label from the SH-sulfur. Moreover, the $\text{SO}_{3}$-sulfur of thiosulfate is recovered largely as sulfate in both the soluble pools and the insoluble fraction, while only a trace of SH-sulfur is recovered as sulfate in either case. Consistent with this, the metabolism of the $\text{SO}_{3}$-sulfur of thiosulfate more closely resembles the metabolism of sulfate. Thus it would appear that exogenous thiosulfate undergoes early dismutation in which the $\text{SO}_{3}$-sulfur is preferentially oxidized, and the SH-sulfur is preferentially incorporated in a reduced state. These results are discussed in relation to the conversion of sulfate to thiosulfate by cell-free extracts of Chlorella previously described.