Biosynthetic mechanism of glycolate in Chromatium IV. Glycolate-glycine transformation

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The metabolic transformation of glycolate to glycine occurring in photosynthesizing cells of Chromatium was investigated by the radioisotopic technique and by amino acid analysis. By analyzing the distribution of radiocarbon upon feeding [1-^<14>C] glycolate, [2-^<14>C] glyoxylate and [1-^<14>C] glycine to bacterial cells, it was demonstrated that glycolate is converted to glycine via glyoxylate, and both glycolate and glycine are excreted extracellularly. Although the formation of serine was barely detected by the above two techniques in both N_2 and O_2 atmospheres, it was found that ^<14>CO_2 is evolved quite markedly from both [1-^<14>C] glycolate and [1-^<14>C] glycine fed to the Chromatium cells. Analytical results of transient changes in amino acid compositions under atmospheric changes of N_2→O_2 and by the addition of exogenous glycolate in N_2 confirm the notion that glycolate is converted to glycine. Acidic amino acids (glutamic acid and aspartic acid) appear to take part in glycine formation as amino donors. The formation of glycine from glycolate in a N_2 atmosphere suggests that an unknown glycolate dehydrogenation reaction may operate in the overall process.
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