Glycollate and glyoxylate excretion by Sphaerocystis schroeteri (Chlorophyceae)

Abstract

Illumination of oxygen-sparged suspensions of Sphaerocystis schroeteri results in the rapid excretion of glyoxylate into the medium. This is followed by the appearance and accumulation of glycollate in the medium. The excreted glyoxylate may be derived from the intracellular enzymic oxidation of glycollate, produced during photorespiration. S. schroeteri possesses a glycollate dehydrogenase and inhibition of this enzyme by α-hydroxy-2-pyridine methanesulphonate stimulates the rate of glycollate excretion and abolishes glyoxylate excretion. The enzyme is susceptible to end-product inhibition by glyoxylate. This compound, produced upon initial exposure of the algae to light, may influence, in turn, whether further glycollate produced is metabolized by S. schroeteri, or excreted.