The function of the Tyr99 residue from Saccharomyces cerevisiae oxidosqualene-lanosterol cyclase (ERG7) was analyzed by constructing deletion, and site-saturated mutants. Two truncated intermediates, (13αH)- isomalabarica-14Z,17E,21-trien-3βol and. (13α\H)-isomalabarica-14Z, 17.E,21.-trien-3β-ol, were isolated from the ERG7Y99X mutants. These results suggest that the functional role of ERG7Y99 is to affect both chair-boat 6-65 tricyclic Markovnikov C-14 cation stabilization and the stereochemistry of the protons at the C-15 position for subsequent deprotonation.
- Reaction mechanisms