Desmosterol
Desmosterol is a lipid present in the membrane of phytoplankton and an intermediate product in cholesterol synthesis in mammal cells. Structurally, desmosterol has a similar backbone to cholesterol, with the exception of an additional double bond in the structure of desmosterol.
The similarity can be seen biologically through the synthesis of cholesterol in the human body, as desmosterol is the immediate precursor to cholesterol in the Bloch pathway. Desmosterol is accumulated in desmosterolosis and undergoes reduction with the enzyme 24-dehydrocholesterol reductase to form cholesterol.
In 2014, desmosterol was named the Molecule of the Year 2012 by the International Society for Molecular and Cell Biology and Biotechnology Protocols and Researches.
Background
Desmosterol is classified as a cholestadienol, a subgroup of a wider known group of sterols, which naturally occur in eukaryotes. The presence of desmosterol in oceans and lakes has the potential to diagnose anoxic conditions and to study trends in steroid chemistry during the early stages of diagenesis. Desmosterol has been found in high yields in samples of Rhizosolenia setigera in Western Svalbard, and from surface sediment off of the Peruvian Shelf sediment-water interface.In 1955, desmosterol was first described and isolated from chick embryo sterol with a 2% yield and was postulated as being a biological precursor to cholesterol by Stokes et al. The first known isolation of desmosterol in invertebrates was published in 1957 by Fagerlund and Idler. This new sterol was isolated in large amounts from balanus glandula, a barnacle species found on the North American Pacific coast. Additionally, small amounts of desmosterol have been found in other crustaceans such as lobster and shrimp in the homarus americanus and pandalus borealis species. This strengthens the conclusion that desmosterol must be created exogenously, as crustaceans have not been seen to biosynthesise sterols.
Biological occurrence
Desmosterol has been largely found within a large population of marine invertebrates. Major sources include barnacles, red algae, annelida, and molluscs. This has led to the idea of an exogenous origin of desmosterol in phytoplankton. In 1967, desmosterol was also identified in large percentages in the red algae Laurencia pinnatifida, Polusiphonia nigrescens, Porphyra purpurea, and dulse after previously having been undetected.In the 1968 paper by Idler, Saito and Wiseman, dulse samples were analysed and the sterols present were determined by gas liquid chromatography. Samples were collected near Grand Manan Island, New York in 1964 and 1965, and showed a significant difference in the presence of desmosterol. Samples 1 and 2 were from the same source, as were samples 3 and 4, and all samples were harvested at different times. Samples 2, 3, and 4 had the major sterol as desmosterol, compared to sample 1, with the major sterol being cholesterol. This indicates a 70% difference in desmosterol composition in the sterol samples over a period of one year. There has been no conclusive evidence to show whether seasonal variation of sterols in barnacles occur.