Detection of dissolved protein molecules in oceanic waters

A method for the extraction and detection of dissolved protein molecules in oceanic waters is described. The procedure involves three separate steps: (1) crude concentration of dissolved protein from seawater by tangential flow ultrafiltration, (2) further concentration and purification of dissolved protein by precipitation with trichloroacetic acid, and (3) separation and detection of dissolved proteins by sodium dodecylsulfate-polyacrylamide gel electrophoresis. Dissolved proteins were successfully extracted with this technique; a relatively limited number of protein molecules (less than 30) were separated and visualized on gels as major bands during the analysis of water from stations located from the subarctic to the tropical Pacific. The majority of proteins had molecular masses ranging from 14 to 66 kilodaltons (kDa). Electrophoretic patterns of dissolved proteins changed both horizontally and vertically in seawater, but some protein molecules were found in all the samples examined. The major proteins detected were relatively pure and were present at high levels. The accumulation of appreciable amounts of a relatively limited number of proteins leads to the hypothesis that particular proteins that make up the majority of the dissolved protein components in seawater are derived from specific sources and contribute quantitatively to the oceanic pool of organic nitrogen.