Dolichol biosynthesis: The occurrence of epoxy dolichol in skipjack tuna liver

Polyisoprenoid alcohols from the livers of temperate sea fish (skipjack tuna, chub mackerel, red sea bream and rainbow trout) were analyzed by using 2D-TLC, electrospray ionization (ESI) mass spectrometry and NMR methods. Dolichols (Dols) were detected in all the fish livers, and they were composed of 19-22 isoprene units with Dol-20 as the predominant prenolog. In addition, Dol-like family compounds were found by using 2D-TLC on skipjack tuna samples. These compounds were found to have a larger molecular mass than the Dol family by 16 mass units. NMR analysis indicated that the Dol-like compounds were consistent with the terminal epoxide structure of Dols (the ω-oxirane derivatives of Dols). ESI analysis also revealed the occurrence of dehydro molecules in both Dols and epoxy Dols (Dol-like) fractions. The occurrence of epoxy Dols in fish is discussed in context with the biosynthesis of Dols, which is responsible for forming Dol phosphate, which lead to Dol-PP-oligosaccharide.