Direct detection and evaluation of conversion of D-methionine into L-methionine in rats by stable isotope methodology

Abstract

The stereoselective kinetics of methionine enantiomers in rats was investigated to evaluate the fraction that converted from D-methionine to the L-enantiomer using a stable isotope methodology. After bolus i.v. administration of D- or L-[2H3]methionine, their plasma concentrations and that of endogenous L-methionine were determined by a stereoselective GC-MS method. L-[2H3]Methionine appeared rapidly after administration of D-[2H3]methionine, whereas D-[ 2H3]methionine was not detected after administration of L-[2H3]methionine. The fraction of conversion of D-[ 2H3]methionine into L-[2H3] methionine was estimated using the area under the plasma concentration vs. time curve of L-[2H3]methionine on D-[2H 3]methionine administration and total clearance of L-[ 2H3]methionine on L-[2H3]methionine administration, and that fraction was >90%. This result demonstrates that almost all i.v. administered D-methionine is converted into the L-enantiomer in vivo. © 2005 American Society for Nutritional Sciences.