The following enzymes catalyze mechanistically related reactions which involve the highly complex cyclic rearrangement of squalene or its 2,3 oxide:

• Lanosterol synthase (EC 5.4.99.7) (oxidosqualene--lanosterol cyclase), which catalyzes the cyclization of (S)-2,3-epoxysqualene to lanosterol, the initial precursor of cholesterol, steroid hormones and vitamin D in vertebrates and of ergosterol in fungi (gene ERG7).
• Cycloartenol synthase (EC 5.4.99.8) (2,3-epoxysqualene--cycloartenol cyclase), a plant enzyme that catalyzes the cyclization of (S)-2,3- epoxysqualene to cycloartenol.
• Hopene synthase (EC 5.4.99.17) (squalene--hopene cyclase), a bacterial enzyme that catalyzes the cyclization of squalene into hopene, a key step in hopanoid (triterpenoid) metabolism.

These enzymes are evolutionary related [1] proteins of about 70 to 85 Kd. As a signature pattern, we selected a highly conserved region which is rich in aromatic residues and which is located in the C-terminal section.