Biosynthesis of sterols in the sea cucumber Stichopus Californicus

Free Sterol Composition of Deep-Sea Holothurian Orphnurgus cf. glaber

The free sterol fraction from the deep-sea holothurian Orphnurgus cf glaber Walsh, 1891, has been isolated and studied by GC–MS. Sterols containing Δ7, Δ0, Δ5, polyunsaturated and 5,8-epidioxy modified cores were found. A high percentage of compounds with polyunsaturated cores distinguish this composition from those of previously studied holothurians. Almost all identified compounds had saturated side chains, which is also a specific feature of this fraction. Peculiarities of biosynthesis and metabolism of the found sterols are discussed.

Balance of Δ5-and Δ7-sterols and stanols in halophytes in connection with salinity tolerance

Sterols (STs) have a key role in regulating the fluidity and permeability of membranes in plants (phytosterols) that have wide structural diversity. We studied the effect of structural STs diversity on salt tolerance in halophytes. Specifically, we used gas chromatography-mass spectrometry (GC-MS), including two-dimensional gas chromatography-mass spectrometry (GCxGC-MS), to assess the STs composition in leaves of 21 species of wild-growing halophytes from four families (Asteraceae, Chenopodiaceae, Plumbaginaceae, Tamaricaceae) and three ecological groups (Euhalophytes (Eu), recretophytes (Re), salt excluders (Ex)). Fifteen molecular species of STs from three main groups, Δ⁵-, Δ⁷-and Δ⁰- STs (stanols), were detected. Plants of the genus Artemisia were characterized by a high content of stigmasterol (30-49% of the total STs), while β-sitosterol was the major compound in two Limonium spp., where it comprised 84-92% of the total STs. Species of Chenopodiaceae were able to accumulate both Δ⁵-and Δ⁷-STs and stanols. The content of the predominant Δ⁵-STs decreased in the order Ex → Re → Eu. Molecular species with a saturated steroid nucleus were identified in Eu and Re, suggesting their special salt-accumulating and salt-releasing functions. The structural analogues of stigmasterol, having a double bond C-22, were stigmasta-7,22-dien-3β-ol (spinasterol) and stigmast-22-en-3β-ol (Δ^7--sitosterol). The ratio of Δ⁵-stigmasterol/Δ⁵-β-sitosterol increased in Ex plants, and spinasterol/Δ^7--sitosterol and 22-stigmastenol/sitostanol increased in Eu plants. These data support the well-known role of stigmasterol and its isomers in plant responses to abiotic and biotic factors. The variability in STs types and their ratios suggested some involvement of the sterol membrane components in plant adaptation to growth conditions. The balance of Δ⁵-, Δ⁷-and stanols, as well as the accumulation of molecular analogues of stigmasterol, was suggested to be associated with salt tolerance of the plant species in this investigation.

Expression and chloroplast targeting of cholesterol oxidase in transgenic tobacco plants

Cholesterol oxidase represents a novel type of insecticidal protein with potent activity against the cotton boll weevil (Anthonomus grandis grandis Boheman). We transformed tobacco (Nicotiana tabacum) plants with the cholesterol oxidase choM gene and expressed cytosolic and chloroplast-targeted versions of the ChoM protein. Transgenic leaf tissues expressing cholesterol oxidase exerted insecticidal activity against boll weevil larvae. Our results indicate that cholesterol oxidase can metabolize phytosterols in vivo when produced cytosolically or when targeted to chloroplasts. The transgenic plants exhibiting cytosolic expression accumulated low levels of saturated sterols known as stanols, and displayed severe developmental aberrations. In contrast, the transgenic plants expressing chloroplast-targeted cholesterol oxidase maintained a greater accumulation of stanols, and appeared phenotypically and developmentally normal. These results are discussed within the context of plant sterol distribution and metabolism.

Biosynthetic studies of marine lipids. 42. Biosynthesis of steroid and triterpenoid metabolites in the sea cucumber Eupentacta fraudatrix

The saponins, conjugated sterols, and free sterols of the sea cucumber Eupentacta fraudatrix were examined. A total of 85 steroids, twelve of them new, were identified in the free sterol, sulfated sterol, and sterol-xyloside fractions. The free sterol fraction contained 4 alpha,14 alpha-dimethylcholest-9(11)-en-3 beta-ol(6) and 14 alpha-methylcholest-9(11)-en-3 beta-ol(7) together with 18 minor sterols. Examination of the aglycone moieties of the sterol-beta-xyloside fraction afforded 31 different sterols. Cholestan-3 beta-ol (15) and 24-methylcholesta-7,22-dien-3 beta-ol (20) were the major sterols in this group. Cholestanol sulfate (74) and cholesterol sulfate (64) were identified as the major components among the 34 different sterol sulfates present. Finally, cucumariosides G1 (1), C1 (2), C2 (3), H (4), and G2 (5) were isolated from the saponin fraction. Radiolabeling experiments indicated that there are two pathways of sterol biosynthesis in E. fraudratix. The first involves transformation of squalene to produce lanosta-9(11),24-dien-3 beta-ol(parkeol) which is subsequently demethylated to form 4 alpha,14 alpha-dimethylcholest-9(11)-en-3 beta-ol (6) and 14 alpha-methylcholest-9(11)-en-3 beta-ol (7). The second proceeds through squalene to lanosterol which is further metabolized to produce the triterpene saponins, 5 alpha-cholest-7-en-3 beta-ol (19) and its xyloside (49).