The Formation of Homoserine from Methionine in Germinating Peas

L-Methionine-1-14C was fed through the roots to 6-day-old pea seedlings. After 10 h over 80% of the absorbed radioactivity was recovered in the free amino acid fraction, 8% in the extracted proteins, 5% as carbon dioxide, and 2.2% in the organic acid fractions. Analysis of the amino acids revealed that only 24% of the total activity was recovered as methionine, 40% as homoserine, 10% as isoleucine, and smaller but significant amounts of aspartate, O-acetylhomoserine, and cystathionine. Dilution values strongly imply that aspartate is not an intermediate in the extensive conversion of methionine to homoserine; rather a more direct pathway is involved.