The Quantitative Analysis of D-Amino Acids in Vegetables and Fruits

Abstract

Various free- and bound- forms of D-amino acids occur not only in bacteria but also in yeast, plants, insects, and mammals. For example, D-alanine and D-glutamate are found as the essential amino acid residues of peptidoglycan in a bacterial cell wall. The bacterial enzymes participating in D-amino acid metabolism, in particular amino acid racemases and D-amino acid aminotransferase, have been studied in detail. Recently the analytical techniques for D- amino acid measurement have developed, and we can rapidly determine various D-amino acids contents in organisms and tissues with high sensitivity to investigate their physiological roles. In marine and euryhaline invertebrates, D-alanine was shown to be involved in the osmotic stress response. In mammals, D-serine acts as a neuromodulator whereas D-aspartate plays various neuronal and endocrine roles. Several D-amino acids were also found in plants, i.e. D-alanine and D-glutamate occur in pea seedling, but their metabolisms and physiological roles are not clarified at all. In this study, we analyzed D-amino acids contents in various vegetables and fruits and examined the biosynthetic pathway of D-amino acid in plant.