Characterization and Dynamic Analysis of Dissolved Proteins in Lake Biwa Using Two-Dimensional Electrophoresis

Concentrated protein-like fluorophores of dissolved organic matter (DOM) in Lake Biwa were analyzed using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and two-dimensional electrophoresis (2-DE). As a result, it was found that the protein-like fluorophores in Lake Biwa are likely to be dissolved proteins released from phytoplankton. SDS-PAGE analysis revealed that protein-like fluorophores from Lake Biwa usually consist of proteins with molecular weights of 33 - 35, 42 - 45, 56 - 59 and 62 - 66 kDa. The molecular weights (MWs) and isoelectric points (pIs) of dissolved proteins in Lake Biwa were firstly clarified using 2-DE. The 2-DE patterns of proteins in Lake Biwa were compared with those for algal DOM released from four kinds of lake phytoplankton, Microcystis aeruginosa, Staurastrum dorsidentiferum, Cryptomonas ovata, and Fragilaria capucina. Some of the protein spots in 2-DE of Lake Biwa were similar to those of algal DOM released during cultivation. The relations between monthly changes in the electrophoretic gel images of lake water samples and those in the community structure of phytoplankton in Lake Biwa were observed. These results suggest that some of the dissolved proteins in Lake Biwa are likely derived from phytoplankton.