Die quantitative Bestimmung vond-Aminos�uren

Determination of amino acid enantiomers in human urine and blood serum by gas chromatography-mass spectrometry

Amino acid (AA) enantiomers were determined as N(O)-pentafluoropropionyl-(2)-propyl esters by chiral gas chromatography-mass spectrometry (GC-MS) in 24 h samples of the urine of three healthy volunteers and in their blood sera. In urine the largest amounts were determined for D-Ser (64-199 micromol/day) and D-Ala (24-138 micromol/day). In blood sera, D-Ala (2.3-4.2 micromol/L) and D-Ser (1.0-2.9 micromol/L) were most abundant. Varying amounts of the D-enantiomers of Thr, Pro, Asx, Glx, Phe, Tyr, Orn and Lys were also found, albeit not in all urines and sera. Further, enantiomers were quantified in urine samples of two volunteers fasting for 115 h. Quantities of renally excreted D-AAs decreased in fasting, although amounts of D-Ser (69 and 77 micromol/L urine) as well as other D-AAs were still detectable. Time-dependent analyses of urine showed that D-AAs are continuously excreted.

D-amino acid utilization in infants measured with the 15N-tracer technique

The utilization rates of D-[15N] valine, D-[15N] leucine, D-[15N] phenylalanine and D-[15N] alanine were investigated in seven infants being fed parenterally. Retention of the (15)N in the protein pool varied from one amino acid to another and ranged from 23.2% for D-[15N] valine to 48.6% for D-[15N] alanine. In the case of valine it was shown that cumulative renal excretion amounted to 70% of the applied (15)N-dose, 44% being overflow of unchanged D-[15N] valine, 16.6% appearing as [15N] urea and 1.2% as [15N] ammonium. This indicates that doubling the concentrations of D-amino acid racemates compared with their L-isomer counterparts in parenteral feeding solutions must inevitably lead to imbalances. The use of D-amino acids for the purposes of parenteral nutrition remains however ineffective due to their poor and variable utilization compared to L-amino acids.