Tryptophan in the sediments of lakes from Southwestern China Plateau

Methods using alkaline hydrolysis and HPLC were first developed to measure tryptophan concentrations in sediments. Early diagenesis of tryptophan was discussed and compared with that of other amino acids. Optimum alkaline hydrolysis conditions (120 °C, 20 h, 4.2 N sodium hydroxide) were chosen to hydrolyze sediments with a tryptophan recovery of 93%. Results show that tryptophan was a minor component in the sediments of four Chinese lakes, its concentrations ranging from 0.15 to 2.66 μmol g−1, and accounted for 0.17–9.18% of total hydrolyzable amino acids (THAA). In terms of relative abundance, tryptophan increased with sediment depth, while the other aromatic species (tyrosine and phenylalanine) decreased, showing contrasting geochemical behaviors among aromatic species during early diagenesis. Based on the good positive correlation between tryptophan and serine, it is suggested that tryptophan may be also related to the selective diatom cell wall preservation.