The interconversion of glycine and serine by plant tissue extracts

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Abstract
Extracts prepared from a variety of higher-plant tissues by ammonium sulphate fractionation were shown to catalyse the intercon-version of glycine and serine. This interconversion had an absolute requirement for tetrahydrofolate and appeared to favor serine formation. The biosynthesis of serine from glycine was studied in more detail with protein fractionated from 15-day-old wheat leaves. Synthesis of [C14]serine from [C14]glycine was not accompanied by labelling of glyoxylate, glycollate or formate. The synthesis of serine from glycine was stimulated by additions of formaldehyde, and [C14]-formaldehyde was readily incorporated into C-3 of serine in the presence of tetrahydrofolate. The results are interpreted as indicating that serine biosynthesis involves a direct cleavage of glycine whereby the a-carbon is transferred via N5N10-methylenetetrahydrofolate to become the [beta]-carbon of serine.