The silicases are a family of enzymes that catalyze rearrangement of silicon-oxygen bonds and are found in some sea sponges.
The by-product of this reaction is silicic acid.
A zinc atom is held in place by three histidine residues. A fourth position on the zinc extracts a hydroxy group from water.
This reacts with an amorphous fragment of hydrated silica to break off silicic acid and leave zinc attached to the larger silica frament.
This is then hydrolysed:
Silicases are related to a more common enzyme in animals, carbonic anhydrase. In the human body the carbonic anhydrase most similar to the sponge silicase is type II (CA-II).