Isoelectric Focusing in Narrow pH Gradients of Kunitz and Bowman-Birk Soybean Trypsin Inhibitors

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Abstract
The two distinct soybean trypsin inhibitors, namely Kunitz and Bowman-Birk inhibitors, were isolated from various commercial sources by isoelectric focusing in the narrow pH 3–6 range in sucrose gradients. The Kunitz inhibitor was also isolated by the same procedure from an aqueous soybean water extract subjected to preparative gel filtration on Sephadex G-25. The Kunitz inhibitor was focused at pH 4.5, and the Bowman-Birk inhibitor at pH 4.3. The two purified proteins were found to be immuno-chemically different. Disc electrofocusing on polyacrylamide gels in the pH 3–10 range was shown to be a simple and high resolution method for detection of heterogeneous preparations of the two inhibitors.