Some Aspects of the Biosynthesis of Phytosterols and Triterpenes

The purpose of this short account is to present some results which cast doubt on the validity of the methods used generally for the study of phytosterol biosynthesis (though not necessarily on the validity of the conclusions arrived at). We shall accept, and not discuss, the present general framework of interpretation of sterol biosynthesis (chart 1) (see for example Goad 1970). Key intermediates, from our point of view, are squalene, squalene epoxide, and a triterpene alcohol: lanosterol in vertebrates and in fungi, cycloartenol in the green plants. The transformation squalene-squalene epoxide is an oxidative step; the transformation squalene epoxidetriterpene alcohol is the biochemical equivalent of an acidcatalysed isomerization.