Cut up 450–500 g of commercial mushrooms and homogenize in 500 ml of distilled water.
Strain off solid residues through gauze.
Centrifuge the liquid at 10–20,000 g and collect the supernatant and allow to stand at 4 °C overnight.
Centrifuge again at high speed.
Collect supernatant and sterilize by filtration. Cellulose membrane filters are not suitable, for obvious reasons. Use asbestos filter mats or similar material (Ford Sterimat or Seitz filters).
Store frozen, in 10–20-ml aliquots.
The crude enzyme can be purified by standard methods for protein purification.