brain tryptophan levels correlated better with plasma trp : neutral amino acid ratios ( r = 0.83 ) than with plasma tryptophan itself ( r = 0.63 ) suggesting that the small changes observed in plasma amino acid profiles were responsible for differences in the brain tryptophan concentrations among the l-tryptophan and tryptophan plastein groups .
C0301715
neutral amino acid
C0002520
amino acid