Ayatollah Mahdi Hadavi Tehrani (may Allah grant him long life):
Animal enzymes are absolutely pure and halal to eat, if they are not, according to the wise men and common view (urf), considered to be a part of the animals. In case they are considered to be a part of the animals, they would be halal in the following cases:
1. They should not be from animals which are essentially impure such as dogs.
2. They should not be included in the category of ritually impure things such semen, urine or feces. [Hence, if they are said to be one of these, they are haram.]
3. The enzymes should have been extracted from living animals or from animals which have been slaughtered in accordance with Islamic law.