Free and attached proteolytic activity in water environments

Size distribution of exoproteolytic activity, as detected by hydrolysis of L-Leucyl-p-Naphthylamide, was studied by differential filtration, ultrafiltration and centrifugation, on natural and enriched samples from the Southern Bight of the North Sea and the Scheldt estuary. Effects of sonication and treatment with Triton X-100 on this size distribution were also investigated. Most exoproteolytic activity in the aquatic environments studied is bound to the envelopes of bacteria. The small fraction (0 to 30 %) of total exoproteolytic activity passing a 0.2 pm filter probably consists of cell fragments, produced upon lysis of bacteria instead of being actively excreted.