Origin of Glycerol Ethers: BIOSYNTHESIS FROM LABELED ACETATE, STEARIC ACID, STEARALDEHYDE, AND STEARYL ALCOHOL

Abstract

Pieces of the digestive gland of the starfish, Asterias forbesi, were incubated in vitro with various radioactive lipid precursors in order to follow the biosynthesis of the alkyl and alkenyl glycerol ethers. Acetate-1-14C was incorporated readily into alkyl glycerol ethers of both neutral lipid and phospholipid fractions, but very poorly into the alkenyl glycerol ethers. Stearic acid-1-14C and stearaldehyde-1-14C were both incorporated into alkyl glycerol ethers, but the fatty aldehyde was a much better precursor of alkenyl glycerol ethers than was the fatty acid. When stearyl alcohol-1-14C-1,1'-3H was compared with stearaldehyde-1-14C-1-3H, it was found, from isotope ratios and relative specific activities, that the fatty aldehyde served as a better precursor than the fatty alcohol in the biosynthesis of alkenyl ethers; on the other hand, the fatty alcohol was more efficiently incorporated into the alkyl ethers. In each of these cases, sufficient tritium was retained on the primary carbon of the lipid product to preclude the obligatory involvement of fatty acids as intermediates in the biosynthesis of lipid ethers. The evidence presented militates against a direct precursor-product relationship between alkyl and alkenyl lipid ethers.