Active form of trypsin was not found in the extract of the pancreas of the catfish Parasilurus asotus. Zymogens were activated autocatalytically to maximal level when the extract was incubated at pH 8.0 and 4°C for 4 days in the presence of calcium ions. The presence of two types of trypsin, anionic and cationic forms, in the autoactivated preparation of the extract was demonstrated by DEAE-cellulose column chromatography. Sephadex G-75 gel filtration and DEAE-cellulose column rechromatography were used for further purification. In the present study, an anionic trypsin was purified to homogeneity. The molecular weight of catfish anionic trypsin was determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and found to be 26,000. The isoelectric point of this enzyme was determined to be 5.4 by isoelectric focusing. The amino acid composition of this enzyme was similar to that of anionic trypsins from some species of vertebrates, including fishes.
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