1. Crystalline urease is not inactivated by trypsin in the absence of a gum. In fact, the presence of trypsin alone in aqueous solutions of urease has an action similar to that of gum, that is, it acts as a "protective colloid" for urease.
2. Crystalline urease is inactivated by trypsin in the presence of a gum. This occurs with great rapidity if purified (crystalline) trypsin is used.
3. If trypsin is added to urease a considerable time before the addition of gum no inactivation of the urease takes place.
4. The suggested explanation is that an inhibitive group of the urease molecule ("antitrypsin") may combine with trypsin to form an irreversible inactive trypsin compound, which cannot attack the urease but has unchanged ureolytic power. This compound cannot be formed if gum is present because the gum has united with a portion of the urease molecule; the tryptic power is thus unimpaired and urease is then digested. This speaks for the protein nature of urease.
