[Resorption and metabolic utilization of D-[alpha-15N]lysine and L-[alpha-15N]lysine after oral administration, with special reference to the metabolism of intestinal bacteria].

Absorption of D-[alpha-15N]lysine and L-[alpha-15N]lysine following an oral single pulse labelling at a dosage of 5 mg 15N'/kg body weight was compared in four subjects aged 4 to 14 months. The wastages of 15N' in the faeces ranged from 0.3 to 5% of the input implying comparably high absorption rates of both the lysine enantiomers. Only about 7.6% of the 15N from the alpha-amino groups were found in the urine after loading with L-[alpha-15N]lysine. In contrast, about 80.2% of the 15N' dose from D-[alpha-15N]lysine were eliminated renally. However, 18.5% of the 15N' dose on an average were retained after D-[alpha-15N]lysine administration. This is certainly due to a partial desamination of D-lysine. The faecal bacteria isolated from the faeces contained no or only small amounts of 15N' after D-[alpha-15N]lysine loading. Following L-[alpha-15N]lysine administration a measurable 15N enrichment of the faecal bacteria of up to 0.09 at % excess was achieved in almost all cases.