[15N transamination in the administration of various tracer substances. 1. Whole body studies in rats]

4 groups of 3 growing Wistar rats each were orally given either 15N methionine, 15N lysine, 15N glycine or 15N ammonia sulphate over 10 days. By means of measuring 15N, the 15N accumulation in the amino acids (AA) of the body protein, statements were to be made on the transamination of the individual 15N substances and thus their suitability as tracer substances for studies of N metabolism. None of the tested 15N AA achieved a proportionate labelling of all AA of the body protein. The AA used as tracer in each case showed the highest 15N labelling of all AA in the body. Of the amino 15N detected in the animal body, ca. 19% were found in Met after a 15N Met application, ca. 88% in Lys after a 15N Lys application and ca. 50% in Gly after a 15N Gly application. After the application of 15N ammonia sulphate ca. 42% of the body amino 15N are apportioned to the essential and ca. 58% to the non-essential AA. Thus this substance produces a more proportional labelling of the essential and non-essential AA of the body protein than 15N Gly. The following quotas of the 15N amounts applied were found in the AA of the animal bodies: tracer substance lysine 52%, glycine 32%, ammonia sulphate 24%, methionine 21%. After summing up the amino acid 15N amounts in the animal body, eliminating in each case the tracer AA and taking into account the molecular weight of the AA, there was a good agreement of the intensity of the accumulation of 15N in the individual AA, irrespective of the applied tracer substance: arginine, glutamic acid, cysteine and aspartic acid highest, threonine, phenylalanine and lysine lowest accumulation.