BIOSYNTHETIC-STUDIES OF MARINE LIPIDS .35. THE DEMONSTRATION OF DENOVO STEROL BIOSYNTHESIS IN SPONGES USING RADIOLABELED ISOPRENOID PRECURSORS

1. De novo sterol biosynthesis in the sponges Tethya aurantia and Aplysina fistularis was investigated, using sodium [5,5-H-3]-mevalonate, [1-H-3]-farnesol and [3-H-3]-squalene. [3-H-3]-Squalene was found to be the best precursor for demonstrating de novo sterol biosynthesis in a wider range of sponges. 2. By feeding [3-H-3]-squalene and using cell-free techniques, the de novo sterol biosynthesis was established in 18 sponges belonging to nine orders. Among these sponges were Axinella polypoides and Axinella verrucosa which had previously been thought to be incapable of de novo sterol biosynthesis based on work with radiolabeled lanosterol, cycloartenol, mevalonate, and acetate. 3. In contrast to earlier assumptions, it is likely that all sponges are capable of de novo sterol biosynthesis.