Charles C. Lund

The binding of l-tryptophan in human plasma at 37 °C☆

Abstract The binding of l -tryptophan in human plasma at 37 °C in the presence and absence of other amino acids and urea was studied. The estimated unbound tryptophan concentration in fasting plasma from binding studies was 18 μmoles/kg. water. This is in good agreement with a mean value of 17 ± 2 obtained from ultrafiltrates of blood at pH 7.4 and 37 °C. Approximately 25% of the total tryptophan is present in fasting plasma as an unbound form. Examples of tryptophan concentrations in some plasmas of simulated small molecule and albumin composition are also given. It is indicated that the concentration of unbound tryptophan is the same in the plasma and the erythrocytes.

Unbound amino acid concentrations in plasma and erythrocytes of normal children and of cord blood.

Abstract Unbound amino acid concentrations were determined in the plasma and erythrocytes of 25 normal children (age 4 days to 12 years) and four cord bloods by the method of salt-saturated paper chromatography. A logarithmic normal distribution was found to be a suitable function for expressing the concentration of the unbound amino acids in the plasma and erythrocytes, whereas a linear normal distribution function was not. By linear and/or exponential regression functions a dependence in which the concentration increased with the age of the child was found for four of the amino acids and ergothioneine. The concentration of the “glutamyl residue” (glutamic acid and glutamine) was found to decrease with the age of the child. The ratio of glutamic acid to glutamine also decreased markedly with age. When compared with adults, many of the childrens values in both components of the blood were significantly lower. The erythrocyte-plasma ratios of the amino acid concentrations were generally higher for the children than for the adults. The ratio for methionine in particular was 1.9 times higher in the children than in the adults. The cord blood amino acid concentrations differed in some respects from both the adult and children bloods. The dibasic amino acids, lysine, ornithine, and histidine, were high in concentration in the cord blood plasma.