Kinetics of intravenously administered 15N-L-alanine in the evaluation of protein turnover.

After a pulse injection of 15N-L-alanine to a healthy male subject, the distribution of 15N in the various components of blood and urine were determined as function of time. The rapid appearance of the isotope both in the urinary urea and ammonia and in the plasma amide and urea suggests that transamination (and not deamination) may be the key step in the interaction. After 30 to 60 min postinjection, the tracer dynamics represents the overall metabolic pool characteristics and does not reflect the metabolism of alanine only. The nitrogen of alanine is used effectively in the synthesis of body protein.