Studies of glycollate utilization and some associated enzymes of C₁ metabolism in the endosperm of Ricinus communis L.

Abstract

Glycollate metabolism in 5-day-old endosperm tissues of Ricinus communis L. was examined by feeding micromolar quantities of [2-¹⁴C]glycollate to tissue slices. It was found that glycollate carbon was rapidly incorporated into glyoxylate, glycine, serine, and carbon dioxide. Only small amounts of ¹⁴C were incorporated into the sugars. Changes in the distribution of ¹⁴C with time suggested that glyoxylate was a primary product and that glycine and serine were secondary products of glycollate metabolism. The results of feeding experiments are interpreted as indicating that a glycollate pathway leading to sugar biosynthesis is of minor importance compared to the rapid utilization of glycollate for the biosynthesis of glycine and serine. Enzymes necessary to catalyse the incorporation of glycollate into glycine and serine have been examined in castor-bean endosperm extracts. These included: glycollic acid oxidase, gloxylic acid reductase, glyoxylate transaminase, N¹⁰ formyltetrahydrofolate synthetase, N⁵,N¹⁰-methylenetetrahydrofolate dehydrogenase, and serine hydroxymethyltransferase.