Comparison of three alkaline proteases from digestive fluid of the silkworm, Bombyx mori L

1. Digestive fluid proteases of the silkworm, 6B1-3, were separated, partially purified and their properties were compared. 2. These proteases were different in the substrate specificity, effect of inhibitors, Km and influence of Mn2+. 3. Hydrolyzing ability for natural substrates was comparatively high in 6B1, whereas the hydrolysis of synthetic substrates of trypsin by 6B1 was lower than that by 6B2 or 3. 4. The protease activity was sensitive to DFP and PMSF. The soybean trypsin inhibitor differentially affected three proteases. Silkworm haemolymph strongly inhibited the protease activity of 6B2 and 3, but scarcely affected 6B1.