A trypsin-like protease was purified from the intestine of flatfish (Paralichthys olivaceus) by gel filtration and anion-exchange chromatography. The molecular weight was estimated to be 29.6 kDa by sodium dodecyl sulfate–polyacrylamide gel electrophoresis. Flatfish protease had maximal activity at 70C and pH 7.5 using N-α-benzoyl-dl-arginine-ρ-nitroanilide as substrate. It was stable to heat treatment up to 50C and to pH ranges between 7.0 and 10.0. It was activated by calcium ion and completely inhibited by mercury ion and known serine-protease inhibitors, such as phenylmethylsulfonyl fluoride, tosyl lysine chloromethyl ketone and benzamidine.
Flatfish trypsin could be an alternative to commercial trypsins in a wide variety of applications in the food, detergent and pharmaceutical industries. In the food industry, trypsin is used to produce protein hydrolysates, extract flavor, tenderize meat and improve oil extractions. It is also used in detergent, bating of leather and in diabetes diagnosis and therapy. Moreover, it can break down tumors and cancer cells in cancer therapy.