Protease activity. The enzyme activity of purified king crab, sardine, salmon, and bovine trypsin was determined by a serine protease assay conducted at room temperature (RT) and 37°C. The protease activity was measured in solutions with increasing protein concentration and results given as mUnits (mU)/μg protein. Total volume of the reaction was 250 μl consisting of 10 μl of purified enzyme and 240 μl of substrate (DL-BAPNA) diluted in substrate buffer. For the measurements at 37°C the substrate buffer was incubated at 37°C for the appropriate time prior to use and the temperature adjusted to 37°C in the chamber of the spectrophotometer.