Cycloartenol-based pathway

Which came first- the lanosterol- or the cycloartenol-based pathway Ourisson et aly suggest that the cycloartenol-based pathway evolved first (9JO). They reasoned that cycloartenol and lanosterol possess different shapes- bent versus flat. The different sterol shapes were discriminated by primitive cells. Both sterols possess a 14-methyl... 

Recent mechanism studies involving incubations with stable isotopes (66,69,70) and studies by us on conformiational analysis (38-42), distribution (7), structure-function/metabolism relationships (54, 55) and mechanistic enzymology of sterol transformation (12,56), negate the otherwise attractive explanation hypothesized by Ourisson et al, (9,10) for evolution of the sterol pathway beginning with the cycloartenol-based pathway. The new data indicate that the lanosterol-based pathway may have evolved before cycloartenol-based pathway, the squalene-oxide cyclase and... 

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