Bile salt evolution.

Viewed against the background of known or supposed biosynthetic pathways for cholic and chenodeoxycholic acids in man and laboratory animals, the chemical nature of bile salts in more primitive animals clearly indicates that evolution from C(27), 5alpha-alcohol sulfates to C(24), 5beta-acids has taken place. Stages in this evolution, some of which are intermediates in the biosynthesis of C(24) bile acids, are described for representatives of all the chief vertebrate groups. "Unique" primary C(24) bile acids may be considered as hydroxylated chenodeoxycholic acids; the possible taxonomic significance of these is discussed. A closer study of the biochemical mechanisms underlying bile salt differences may be expected to throw new light on the nature of the evolutionary process itself.