Abstract
1. A number of pepsin solutions containing several protein components have been studied by the electrophoresis method. All samples show a homogeneous boundary moving to the anode at pH 4.4. 2. The activity of this material may be higher than that of the original solution on the basis of total nitrogen but is the same as that of the original solution on the basis of protein nitrogen. 3. There is no separation of the various protein components under these conditions. 4. The apparent isoelectric point at pH 2.7, previously obtained by the collodion particle method is due to the presence of decomposition products. Pure crystalline pepsin, free from decomposition products, is always negatively charged.