The following enzymes catalyze mechanistically related reactions which involve
the highly complex cyclic rearrangement of squalene or its 2,3 oxide:
Lanosterol synthase (EC 126.96.36.199) (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 188.8.131.52) (2,3-epoxysqualene--cycloartenol
cyclase), a plant enzyme that catalyzes the cyclization of (S)-2,3-
epoxysqualene to cycloartenol.
Hopene synthase (EC 184.108.40.206) (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  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.
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