Hydrolysis of peptides in seawater and sediment

Protein hydrolysis and subsequent peptide production appear to be the links between degradation of protein and production of free amino acids in the marine environment. This model has not yet been fully demonstrated because neither presence of peptides nor peptide hydrolysis has been directly measured in seawater or sediments. Fluorescent Lucifer Yellow (LYA)-derivatives of several peptides were synthesized and tested for use as models in an investigation of peptide hydrolysis in seawater and sediment. We demonstrated that these LYA-derivatives behave to some degree as the natural peptides by showing that LYA-dialanine effectively competes with dialanine (ala2) for the active sites of microbial hydrolytic enzymes found in seawater. LYA-derivatives of ala2, ala-leu and ala4 hydrolyzed to smaller peptides or free amino acids in both seawater and sediments. In seawater, hydrolysis of the longer peptide, LYA-ala4 was 90 × faster than hydrolysis of LYA-ala2 and 30 × faster than LYA-ala-leu. In sediments, rapid disappearance of the initially-added substrate LYA-ala4 from pore waters was followed by slower production of LYA-ala3, LYA-ala2 and LYA-ala. Hydrolysis was not random; preferential cleavage of certain peptide bonds occurred.