Serial monthly peptidase activities were assayed in the surface water of Lake Shinryu, located in the Chugoku district of Japan, using artificial fluorescent peptidase substrates. The results indicated that the lake water had higher aminopeptidase activities than endopeptidase activities except in November and December, whereas lake water filtrated using membranes with a pore size of 0.2 μm showed higher endopeptidase activities than aminopeptidase activities from June to December, with peaks in June and November. The serial aminopeptidase activity profile was relatively similar to that of the chlorophyll-a concentration. The size distribution of aminopeptidase activities indicated that half of the total activity was retained in the fraction between 5 and 100 μm. These results suggest that phytoplankton participate in the digestion of peptides with aminopeptidase activities. Electrophoretic analysis detected the presence of three peptidase bands (1, 2, and 3) in the lake water that passed through the 0.2-μm membranes. Samples from June, September, and November dominantly contained these active bands in different electrophoretic profiles.
Peptidase Phytoplankton Peptidase zymograph Electrophoresis Lake Shinryu
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We are grateful to Dr. T. Ohtsuka, Lake Biwa Museum, for species identification. This work was supported in part by a Grant-in-Aid (No. 19510012) for Scientific Research from the Ministry of Education, Sports, Science, and Culture of Japan (to Nakamura) and River Environmental Funds (No. 20-1215-027 and 22-1211-032) in charge of the Foundation of River and Watershed Environment Management, Japan (to Nakamura).
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