Trypsin from the viscera of S. basilisca was extracted and purified successively by the four-step procedure described in Section 2. In the first step, the crude enzyme extract was fractionated with ammonium sulphate. The precipitate formed at 40–80% (w/v) saturation showed higher specific activity (0.23 U/mg of protein), than the precipitate formed at 0–40% saturation (0.05 U/mg of protein). No activity was detected in the final supernatant. The 40–80% fraction, which gave the highest specific activity, was then subjected to Sephadex G-100 gel filtration. This procedure yielded one peak of protease activity (BAPNA) (Fig. 1a). Fractions showing trypsin activity were pooled and then loaded on a Mono Q-Sepharose
anion-exchange chromatography column that had been equilibrated with buffer C. Binding proteins were eluted with a linear gradient of NaCl (0–0.5 M). BAPNA activity appeared in a single peak (Fig. 1b). Finally the active fractions were concentrated by ultrafiltration. The results of the purification procedure are summarised in Table 1. After the final purification step, the trypsin was purified 4.2-fold, with a recovery of 12% and a specific activity of 0.5 U/mg of protein, using BAPNA as a substrate.