Sterols in Echinodermata starfish

The major sterols of Echinodermata are C27-sterols. Cholesterol is the principal sterol in echinoids (70-80%), ophiuroids, and crinoids. 5a-Cholest-7-en-3i8-ol is the major sterol in asteroids and sea cucumbers. A C26-sterol, 24-norcholesta-5,22-dien-3 8-01 (83) is also a common sterol in Echinodermata the content is especially high (6-10%) in ophiuroids and crinoids [79]. Asterosterol (70), a A -C26-sterol, is common in asteroids and sea cucumbers [80], and amuresterol (71) was isolated from Asterias amurensis [81]. 

Acanthasterol [82] (acansterol) [83,84] (72), the isomer of gorgosterol, was isolated from Acanthaster planci by Scheuer. Gorgostanol [85] and demethyl-acanthasterol (73) [86] were also found in A. planci [86] (Fig. 8). Transformation from A - to A -sterol may be a common bioconversion in Echinodermata, because gorgonians are components of the diet of A. planci in which gorgosterol cannot be found. 

In addition to cholesterol and 5a-cholest-7-en-3y8-ol, many C2g and C29 conventional sterols are present in Echinodermata. These sterols are probably derived from the diet. However, echinoderms are able to synthesize sterols. Thus, [ C]mevalonic acid was incorporated into squalene, lanosterol and desmosterol by the sea urchin. Echinus esculentus [87]. The ability of ophiurpids to synthesize sterol from [ C]acetate has also been demonstrated [88]. Sterol biosynthesis by a holothuroid was first investigated by Numura [89], and sterol biosynthesis from [ C]acetate in sea cucumbers has also been reported [90]. 

The ability of starfish to synthesis sterols was first demonstrated by Smith and Goad, who found a slow incorporation of [ C]mevalonate into 4-desmethylsterols [91]. The main labelled sterol in A. rubens was 5a-cholest-7-en-3 8-ol [92]. Evidence 

Estradiol and progesterone have been tentatively identified in extracts of ovaries of the starfish Pisaster ochraceus [93] and the sea urchin Stronglyocentrotus fran-ciscanus [94]. Progesterone was also identified in the ovaries of the starfish Asterias amurensis by Ikegami [95]. The physiological role of progesterone in starfish ovaries is unknown, but probably is connected with oocyte maturation. 

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