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A total of 34 dipeptides was detected in water extract of the recent sediment core S8602 of Tokyo Bay by gas chromatography coupled to mass spectrometry. These dipeptides were indigenous to the sediments and showed predominance of the L or LL stereoisomers indicating that they were derived mainly from proteins. Alanylalanine, valylalanine, alanylleucine, and alanylaspartic acid were the four most abundant dipeptides, and their individual concentrations were about 5 nmol g-1 at 1.3 cm in depth. All dipeptides showed a maximum concentration at 1.3 or 6.3 cm in depth, which decreased rapidly with depth especially over a depth range from 6.3 to 13.8 cm. Total concentration of dipeptides at 1.3 cm in depth, corresponding to 160 nmol g-1 for amino acid residues, accounted for 2.8% of the hydrolyzed amino acids, and was about 1.2 times larger than that of free amino acids in the same water extract. Accordingly, dipeptides are one of the major products as well as free amino acids during the earliest stage of protein degradation in sediments. On the other hand, diketopiperazines were not found in the sediments. In addition, the sequential isomeric ratios of some dipeptides differed from the reported ratios at equilibria. Therefore, dipeptides were not derived through diketopiperazines and likely preserved their original amino acid sequences in their precursor proteins.

Detection of water extractable dipeptides and their characteristics in recent sediments of Tokyo Bay.