Studies on proteinases from the digestive organs of sardine. I. Purification and characterization of three alkaline proteinases from the pyloric caeca.

Three alkaline proteinases designated I, II and III are found in the pyloric caeca of sardine and isolated by (NH4)2SO4 fractionation, DEAE-cellulose chromatography and gel filtration on Sephadex G-100. The final preparations were judged homogeneous by multiple criteria. The molecular weights of the enzymes I, II and III were determined by the sedimentation equilibrium method to be 22 900, 28 700 and 27 000, respectively. The isoelectric points were 5.45, 5.30 and 4.85, and the sedimentation coefficients (S0 20, w) were 2.91, 3.06 and 2.94, respectively. Enzymes II and III had similar amino acid compositions which were different from that of enzyme I, especially in the content of lysine, valine and tyrosine. All the enzymes belonged to a group of serine proteases. Enzymes II and III were found to be an anionic alpha-chymotrypsin-like enzymme and an anionic trypsin-like enzyme, respectively. Although these fish enzymes had properties in common with those of bovine pancreatic cationic trypsin and chymotrypsin, they are distinctly different in their optimum pH, pH stability, net charge and immunological properties.