THE TRANSPORT AND METABOLISM OF GLYCOLIC ACID BY CHLAMYDOMONAS REINHARDTII

In order to understand the excretion of glycolate from Chlamydomonas reinhardtii, the conditions affecting glycolate synthesis and metabolism were investigated. Although glycolate is synthesized only in the light, the metabolism occurs in the light and dark with greater metabolism in the light due to refixation of photorespiratory CO{dollar}sb2{dollar}. The amount of internal glycolate will affect the metabolism of externally added glycolate. When glycolate synthesis exceeds the metabolic capacity, glycolate is excreted from the cell.; Treatment of leaves from higher plants with aminooxyacetate leads to severe inhibition of CO{dollar}sb2{dollar} fixation. Since CO{dollar}sb2{dollar} fixation by isolated chloroplasts was increased by incubation with aminooxyacetate, the inhibition is not due to an effect on reactions within the chloroplasts. Therefore, accumulation of some inhibitory metabolite may be occurring in higher plants and excretion of glycolate by algae may be a protective mechanism.; The transport of glycolate into the cells occurs very rapidly. Equilibrium is achieved at 4{dollar}spcirc{dollar}C within the time cells are pelleted by the silicone oil centrifugation technique through a layer of ({dollar}sp{lcub}14{rcub}{dollar}C) glycolate. Glycolate uptake does not show the same time, temperature and pH dependencies as diffusion of benzoate. Uptake can be inhibited by treatment of cells with N-ethylmaleimide and stimulated in the presence of valinomycin/KCl. Acetate and lactate are taken up as quickly as glycolate. The hypothesis was made that glycolate is transported by a protein carrier that transports monocarboxylic acids. The equilibrium concentration of glycolate is dependent on the cell density, implying that there may be a large number of transporter sites and that uptake is limited by substrate availability.; A search for a mutant in this transporter was made using survival on fluoroacetate as a screen. All 48 mutants isolated were deficient in acetate metabolism and were unable to utilize acetate heterotrophically. One mutant isolated had reduced acetate and glycolate uptake and is a possible transport mutant. Wild-type Chlamydomonas reinhardtii strain 137 cells do have isocitrate lyase and malate synthase activity when grown photoautotrophically and the activities are increased in the presence of acetate. The mutants were divided into 6 classes based on the levels of isocitrate lyase and malate synthase when grown phototrophically in the presence of acetate.