Characterization of water-extractable amino acids in the sub-surface of semi-permafrost environments

Terrestrial core samples of semi-permafrost sediment were analyzed for total free amino acids (TFAA). The TFAA content ranged from 12.0 to 462.0 nmol/g of sediment, and generally consisted of protein amino acids as the most abundant component of TFAA. The depth profiles in terms of the content drastically decreased with the depth, followed by the vertical distribution patterns of total hydrolyzed amino acids (THAA) within the same sediment. The abundance of THAA was 14 to 327 times larger than that of TFAA. Plots of TFAA versus THAA values yielded a straight line, as defined by the equation THAA = 10.1 x TFAA^1.4 (R^2 = 0.86) based on the least-squares method. The molar ratio of β-alanine and γ-aminobutyric acid did not increase with the depth via diagenesis, as was the case in the THAA fraction. On the other hand, the molar ratio of basic amino acids such as histidine and ornithine gradually decreased with increasing depth. The present study determined that the major organic matter content in the sediment consisted not of free, but bound amino acid analogs.