EFFECT OF ADDING BRANCHED-CHAIN AMINO-ACIDS TO A NICOTINIC ACID-FREE, LOW-PROTEIN DIET ON THE CONVERSION RATIO OF TRYPTOPHAN TO NICOTINAMIDE IN RATS

The effects of adding branched-chain amino acids to a nicotinic acid-free, low-protein diet on the conversion of tryptophan to nicotinamide were investigated in rats. The conversion ratio [urinary excretion of nicotinamide and its metabolites (mu mol/day)x100/tryptophan intake during urine collection (mu mol/day)] was significantly lower in the groups fed with the 3% Leu-, Val-, or Ile-added diet than in the group fed with the control diet. Namely, the inhibition of this conversion was observed not only by the addition of Leu, but also by the addition of Val or Ile. The addition of Ile and/or Val to the Leu-added diet did not antagonize the Leu effect.