Aspects of D-leucine and D-lysine metabolism in maize and ryegrass seedlings

Abstract

Maize and ryegrass seedlings (2.5 weeks old), the roots of which were dipped into 10(-3)M (14)C-carboxyl-labeled D-leucine and (14)C-ε-labeled D-lysine, readyly absorbed and converted or conjugated within 34 hr some 75-90% of the labeled compound supplied. The metabolic intermediates and products were generally similar for both maize and ryegrass. Radioactive intermediates from the carboxyllabeled D-leucine were L-leucine, N-malonyl-D-leucine (provisionally identified), and α-ketoisocaproic acid. Intermediates from ε-labeled D-lysine were numerous, with greater amounts and numbers detected in roots than in tops. Pipecolic acid was a major intermediate particularly in shoot tissue.Pathways of conversion appeared analogous to those for the L-isomer, and conversion may be by the usual L-configuration machinery, since the labeled L-isomer of the originally supplied (14)C-D-amino acid was always found. How the (14)C-D-amino acid gets to (14)C-L-isomer is not known, but finding significant proportions of unlabeled D-alanine in plants treated with both the labeled L-leucine and D-lysine suggested that formation of the α-keto-acid analog and subsequent reamination was possibly an important route.