Direct evidence for synthesis of valine in man

Plasma valine and 13C-valine concentrations were measured in 2 healthy volunteers and 2 uraemic patients during and after a 3-hour intravenous infusion of the 13-c-labelled alpha-keto-acid analogue of valine. Plasma-valine increased by 23-43%. 13C-valine accounted for most of the early increase, but for less than 30% of the increase 1 hour after infusion. It was concluded that valine had increased by 2 mechanisms with different time courses. Initially, transamination of the infused ketoacid predominated, confirming directly for the first time that the essential aminoacid valine can be synthesised in-vivo both in health and uraemia. The previously unsuspected second mechanism was quantitatively more important but slower in ooperation; it may prove to be the key to understanding the metabolic effects of essential aminoacid precursors.