Peptide hydrolysis and uptake of peptide hydrolysis products in the James River estuary and lower Chesapeake Bay

The lability of small peptides was investigated along the salinity gradient of the James River estuary and lower Chesapeake Bay using two fluorescent analogs, Lucifer Yellow Anhydride-alanine-valine-phenylalanine-alanine (LYA-AVFA) and LYA-tetraalanine (LYA-AlA4). Hydrolysis rates of these compounds were compared with each other, and with uptake rates of potential hydrolysis products and other smaller derivatives (e.g., glutamic acid and dialanine). Results suggest that rates of peptide hydrolysis and uptake of hydrolysis products were not always correlated with each other along the salinity gradient, or to other environmental parameters measured in the James River and lower Chesapeake Bay. This may be because diverse input and removal processes can influence both peptide hydrolysis and uptake, but not necessarily simultaneously. Rates of both peptide hydrolysis and free amino acid uptake were strongly associated with particles, particularly those freshly produced. This suggests more rapid turnover of enzymatically available organic nitrogen in regions with elevated phytoplankton biomass. Changes in the abundance and composition of dissolved amino acids in these waters were also examined. Dissolved amino acid compositions, but not concentrations, varied with salinity along a gradient from the tidal fresh James River to the mouth of Chesapeake Bay. These compositional variations demonstrate the mixing of terrestrial organic nitrogen and in-situ production along the salinity transect.