Carbon Metabolism of C14-Labeled Amino Acids in Wheat Leaves. III. Further Studies on the Role of Serine in Glycine Metabolism

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Abstract
When wheat leaves were fed with glycine-2-C14, serine-1-C14, or serine-3-C14, a considerable amount of the label was incorporated into the acidic components of the alcohol soluble substances. Among the acidic compounds, an unknown compound was identified tentatively as a guanine derivative It is a derivative of guanylic acid, but is not a free guanosine mono-, di-, or triphosphate. Both glycine and serine served as effective precursors of the guanine derivative. All of the C14 in this compound was found in the guanine moiety. Glyceric acid from experiments performed in the light contained more C14 than glycolic acid, but the reverse was true when experiments were performed in the dark. As the feeding time was increased in the light, malic acid and the guanine derivative became the 2 most radioactive compounds among the acidic components. In contrast, malic acid from experiments performed in the dark possessed much less C14 than in the light. On the other hand, the amount of C14 in the guanine derivative remained more or less the same. The effect of glycolate on the metabolism of glycine-2-cl4 in the dark was investigated. In the presence of unlabeled glycolate, the C14 from glycine-2-Cl4 was incorporated rapidly into an unknown compound which contained nearly half the total C14 in the acidic fraction. The distribution of C14 among the other acidic components appeared to be similar to that resulting from experiments with glycine-2-cl4, serine-1-C14, or serine-3-C14 alone.