Aminooxyacetate Stimulation of Glycolate Formation and Excretion by Chlamydomonas

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Abstract
Aminooxyacetate (1 millimolar) did not inhibit photosynthetic 14CO2 fixation by Chlamydomonas reinhardtii Dangeard, (−) strain (N.90) but greatly stimulated the biosynthesis and excretion of glycolate. Similar results were obtained from cells grown with 5% CO2 or low CO2 (air). After 2 minutes with air-grown cells, [14C]glycolate increased from 0.3% of the total 14C fixed by the control to 11.7% in the presence of aminooxyacetate and after 10 minutes from 3.8% to 41.1%. Ammonium nitrate (0.2 millimolar) in the media blocked the aminooxyacetate stimulation of glycolate excretion. Chromatographic analyses of the labeled products in the cells and supernatant media indicated that aminooxyacetate also completely inhibited the labeling of alanine while some pyruvate accumulated and was excreted. A high percentage (35%) of initial 14CO2 fixation was into C4 acids. Initial products of 14CO2 fixation included phosphate esters as well as malate, aspartate, and glutamate in treated or untreated cells. Lactate was also a major early product of photosynthesis, and its labeling was reduced by aminooxyacetate. Inasmuch as lactate was not excreted, glycolate excretion seemed to be specific. When photosynthesis was inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea, labeled organic and amino acids but not phosphate esters were lost from the cells. Aminooxyacetate did not inhibit the enzymes associated with glycolate synthesis from ribulose bisphosphate.