Dissolved protein fluorescence in two Maine estuaries

Fluorescence of dissolved proteinaceous materials was examined in two estuaries differing primarily in river input. Low-wavelength excitation (220–230 nm) was found to be more useful than the high-wavelength excitation (280 nm) usually reported in the literature. Levels of fluorescence in estuarine samples were of the order to be expected from the probable levels of dissolved amino acids. However, quantitation of protein levels by fluorescence, even in relative terms, is virtually impossible, due to positive interferences among the two amino acid peaks and humic material and negative interference by various types of quenching. Salinity has little or no effect on quantum yield. Proteinaceous fluorescence along estuarine transects was noisy, with some positive correlations with chlorophyll levels. Noisy data are consistent with the short lifetimes of proteins in seawater. Sediments appeared to provide a source of proteinaceous fluorescence. Seaward samples tended to show higher tyrosine peaks while upstream samples were richer in tryptophan emission.