Glycolate metabolism in cyanobacteria. III. Nitrogen controls excretion and metabolism of glycolate in Anabaena cylindrica |
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Authors: | Eva Renströ m-Kellner,Birgitta Bergman |
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Affiliation: | Dept, of physiological Botany, Univ., of Uppsala, Box 540, S-751 21 Uppsala, Sweden |
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Abstract: | The effect of nitrogen on excretion and metabolism of glycolate in Anabaena cylindrica (CCAP 1403/2a) was studied. Glycidate, an inhibitor of glutamate:glyoxylate aminotransferase (EC 2.6.1.4), reduced the L-methionine-DL-sulfoximine-induced NH4+ release by ca 40%, while net CO2 fixation and C2H2 reduction were not lowered. This indicates that at least a part of the glyoxylate synthesized in A. cylindrica is metabolized via glycine to serine. Addition of NH4Cl or glutamate to the medium reduced the excretion of glycolate. At pH 9, under air, NH4Cl reduced the excretion by 10–30% and under high pO2 (0.03 kPa CO2 in O2) by about 80–90%. At pH 7.5, under high pO2, NH4Cl and glulamate reduced the excretion by about 40 and 80%, respectively. Also, the presence of NH4Cl stimulated the animation of glyoxylate under such conditions as shown by an increased glycine pool and a decreased glutamate pool. We suggest that nitrogen regulates the capacity of A. cylindrica to retain and recycle glycolate intracellularly and that glutamate serves as an amino donor in the conversion of glyoxylate to glycine. |
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Keywords: | Anabaena cylindrica cyanobacteria glutamate glyoxylate aminotransferase glycidate glycolate L-methionine-DL-sulfoximine |
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