Three serine proteinases designated as proteinases A, B and C were purified 800 to 2, 000-fold from an extract of Euphausia superba with an affinity column of soybean trypsin inhibitor (STI)-Sepharose 4B, and by gel filtration on Sephadex G-75 and DEAE-cellulose chromatography. The final preparations except for proteinase A were electrophoretically homogenous. The molecular weights of enzymes A, B and C were determined to be 28, 000-30, 000. Enzymes B and C showed very similar amino acid compositions in which acidic amino acids were abundant. Enzymes A, B and C could hydrolyze protein substrates and synthetic ester substrates including arginine residues. But they hydrolyzed most of the substrates more slowly than bovine trypsin did. All the enzymes were inhibited by soybean trypsin inhibitor, diisopropyl-fluorophosphate, leupeptin and antipain.Their enzymatic and molecular properties such as an instability in an acidic pH region, molecular weight and amino acid composition were similar to those of fish trypsin-like enzymes although krill enzymes had very low isoelectric points (pI 2.6).
These results suggest proteinases A, B and C in Antarctic krill are anionic trypsin-like enzymes and different from the well known cathionic trypsins in mammals.

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