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| Description: Catalyzed by squalene synthase. Dissociation of the PPi group on one of the molecules of farnesyl-PPi yields an allylic carbocation. The double bond nucleophilically attacks the carbocation, forming a tertiary cation at C3 of the first farnesyl-PPi. Loss of a proton from C1 gives the activated cyclopropane intermediate, presqualene-PPi. Dissociation of the second pyrophosphate leads to rearrangement and formation of another tertiary carbocation intermediate. Hydride transfer from NADPH completes the rearrangement, giving squalene. Picture Stats: Views: 174 Filesize: 76.45kB Height: 784 Width: 425 Source: https://biology-forums.com/index.php?action=gallery;sa=view;id=34677 |