On the mechanism of enzyme action. XLVI. The effect of certain ions on crystalline trypsin and reinvestigation of its isoelectric point

Calcium and manganese ions are effective protectors of crystalline trypsin in alkaline solutions. Other ions seem to have no significant influence. The effect of calcium is due to a decrease in the rate of autodigestion of trypsin but does not affect the rate of tryptic digestion of other proteins. The isoelectric point of trypsin is in the neighborhood of pH 11, as determined by electrophoresis analyses. This high isoelectric point is correlated with the amino acid composition of trypsin and its amide nitrogen content.