The degree of conversion of alpha-keto acids to valine and phenylalanine in health and uraemia.

13C-labelled alpha-keto acid analogues of valine and phenylalanine were given by mouth and by intravenous route to three healthy and four uraemic individuals who were used as their own controls. The excretion of 13CO2 in expired air and of 13C-labelled keto acid in urine was measured together with plasma and, in some cases, intramuscular concentrations of total and 13C-labelled free valine and phenylalanine. A minimum and maximum limit of degree of conversion of these two alpha-keto acids to essential amino acids were calculated and was of the order of 25-50 per cent for both keto acids given by either route in health and uraemia.