Crystallization of Pepsin from Alcohol

1. Pepsin is soluble in 65 per cent alcohol and may be readily crystallized from 20 per cent alcohol. The crystals appear as needles or plates which may be transformed into the usual hexagonal bipyramids by recrystallization from water. The different crystals are probably two crystalline forms of the same chemical substance. 2. The enzyme is quite stable in 20 per cent alcohol at pH 2.0 but is inactivated by high concentrations of alcohol. 3. The enzyme is stable for several hours in 65 per cent alcohol at pH 4.0 to 5.0 but is rapidly inactivated in more acid solution. 4. No increase in activity could be noted after treatment with hydrogen peroxide. 5. No proteolytic activity either before or after treatment with hydrogen peroxide could be found in trichloracetic acid filtrates, butyl alcohol extracts of pepsin preparations, or oxidized phenylhydrazine solutions.