Isoelectric focusing of Protac, the protein C activator from copperhead (Agkistrodon contortrix) venom: a note on experimental problems.

The isoelectric point of Protac was recently estimated to be at pH 3. However, further investigations using different experimental procedures revealed that Protac, due to its particular binding properties, is able to form complexes with carrier ampholytes. Thus, the actual isoelectric point of Protac was found to be in the basic region.