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Updated: Oct 17, 2026

Unraveling Entropic Rate Acceleration Induced by Solvent Dynamics in Membrane Enzymes
Published on: January 16, 2016
Conserved tyr residues determine functions of Alicyclobacillus acidocaldarius squalene-hopene cyclase
1Microbiologie/Biotechnologie, Universität Tübingen, Auf der Morgenstelle 28, D-72076, Tübingen, Germany.
Abstract:
The catalytic cavity of Alicyclobacillus acidocaldarius squalene-hopene cyclase is mainly lined by aromatic amino acids. In recombinant cyclases, three out of four tyrosine residues (Y) have been mutated to phenylalanine residues (F). The mutant cyclases Y495F and Y612F had less activity than the wild-type cyclase, but a wild-type product pattern. Mutant Y609F had wild-type activity but a drastically altered product pattern with hopene and significant amounts of bicyclic alpha-polypodatetraene and different tetracyclic triterpenes (dammaradienes and eupha-7,24-diene). The experiments demonstrated that Y495 and Y612 may be involved in the initiation of the cyclization reaction and Y609 in the stabilization and/or positioning of the intermediate carbocations.
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