THEa first investigation of the behaviour of pepsin in an electric field was pub- lished by Michaelis & Davidsohn [1910]. They attempted to determine the sign of the charge on commercial pepsin ("purissimum Grubler") in the pH range 1 04-3, using the well-known Michaelis transference apparatus. After passing current through the apparatus, qualitative tests were made for pepsin in the compartments above the stopcocks. They found that pepsin is negatively charged at pH >37, positively charged at pH <2-0, and within this interval shows migration towards both sides. This latter phenomenon was also observed at very acid reaction (0.1 N HCO). The isoelectric point, obtained by taking the average of the hydrogen ion concentrations corresponding to the pH limits mentioned, is given as cH+ 5.5 x 10-3, or pH = 2 25.
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Tiselius et al. (1938) studied this question.
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