Role of sterols in membranes

Nes, William R.

doi:10.1007/bf02532509

Cited by 263 publications

(88 citation statements)

References 136 publications

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“…b-Sitosterol is the dominant biomarker in this part of the core. It is a non-specific phytosterol generally found in vascular plants (Scheuer, 1973;Nes, 1974;Killops and Killops, 2005), and since its concentration profile is comparable to abundance profiles of Hydrocotyle, Cyperaceae and Amaranthaceae, here it seems mainly derived from shrubs. The pinkish white to pale brown mud in this basal part of the record, dominated by nonmarine ostracodes and molluscs, was interpreted by Cronin et al (2007) as lacustrine.…”

Section: Early-holocene Terrestrial Environmentmentioning

confidence: 86%

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Late Holocene sea-level rise in Tampa Bay: Integrated reconstruction using biomarkers, pollen, organic-walled dinoflagellate cysts, and diatoms

Soelen

Lammertsma

Cremer³

et al. 2010

Estuarine, Coastal and Shelf Science

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a b s t r a c tA suite of organic geochemical, micropaleontological and palynological proxies was applied to sediments from Southwest Florida, to study the Holocene environmental changes associated with sea-level rise. Sediments were recovered from Hillsborough Bay, part of Tampa Bay, and studied using biomarkers, pollen, organic-walled dinoflagellate cysts and diatoms. Analyses show that the site flooded around 7.5 ka as a consequence of Holocene transgression, progressively turning a fresh/brackish marl-marsh into a shallow, restricted marine environment. Immediately after the marine transgression started, limited water circulation and high amounts of runoff caused stratification of the water column. A shift in dinocysts and diatom assemblages to more marine species, increasing concentrations of marine biomarkers and a shift in the Diol Index indicate increasing salinity between 7.5 ka and the present, which is likely a consequence of progressing sea-level rise. Reconstructed sea surface temperatures for the past 4 kyrs are between 25 and 26 C, and indicate stable temperatures during the Late Holocene. A sharp increase in sedimentation rate in the top w50 cm of the core is attributed to human impact. The results are in agreement with parallel studies from the area, but this study further refines the environmental reconstructions having the advantage of simultaneously investigating changes in the terrestrial and marine environment.

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Section: Early-holocene Terrestrial Environmentmentioning

confidence: 86%

“…Friedelanone, like b-sitosterol, originates from vascular plants (Scheuer, 1973;Nes, 1974;Killops and Killops, 2005). Possibly, b-sitosterol represents local herbaceous vegetation, which disappears when the environment becomes brackish.…”

Section: Mid and Late Holocene Marine Transgressionmentioning

confidence: 99%

Late Holocene sea-level rise in Tampa Bay: Integrated reconstruction using biomarkers, pollen, organic-walled dinoflagellate cysts, and diatoms

Soelen

Lammertsma

Cremer³

et al. 2010

Estuarine, Coastal and Shelf Science

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“…True sterols-e.g., end products such as cholesterolare antedated by the production of sterol-like compoundse.g., pentacyclic triterpenoids (3-6)-which were formed in the Precambrian anaerobic environment by the cyclization of squalene. Once molecular oxygen was in sufficient quantity in the atmosphere to permit squalene oxide genesis, a switching mechanism became operative to divert squalene from pentacyclic triterpenoid production to sterol synthesis (6,7). The first compounds derived by the anaerobic cyclization of squalene oxide are the tetracyclic stereoisomers cycloartenol and lanosterol.…”

Section: Route Operates In IImentioning

confidence: 99%

Sterol phylogenesis and algal evolution.

Nes¹,

Norton²,

Crumley³

et al. 1990

Proc. Natl. Acad. Sci. U.S.A.

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The stereochemistry of several sterol precursors and end products synthesized by two fungal-like microorganisms Prototheca wickerhamii (I) and Dictyostelium discoideum (H) have been determined by chromatographic (TLC, GLC, and HPLC) and spectral (UV, MS,-and 'H NMR) methods. From I and H the following sterols were isolated from the cells : cycloartenol, cyclolaudenol, 24(28)-methylenecycloartanol, ergosterol, protothecasterol, 4a-methylergostanol, 4a-methylclionastanol, clionastanol, 2413-ethylcholesta-8,22-enol, and dictyosterol. In addition, the mechanism of C-24 methylation was investigated in both organisms by feeding to I[2-3H]lanosterol, [2-3H] Based on what is known in the literature regarding sterol distribution and phylogenesis together with our rmdings that the stereochemical outcome of squalene oxide cyclization leads to the production of cycloartenol rather than lanosterol (characteristic of the fungal genealogy) and the chirality of the C-24 alkyl group is similar in the two nonphotosynthetic microbes (Ji oriented), we conclude that Prototheca is an apoplastic Chlorelia (i.e., an alga) and that Dictyostelium as well as the other soil amoebae that synthesize cycloartenol evolved from algal rather than fungal ancestors.The sterol pathway is thought to be very ancient, perhaps having arisen during the later stages of prokaryote evolution (1, 2). True sterols-e.g., end products such as cholesterolare antedated by the production of sterol-like compoundse.g., pentacyclic triterpenoids (3-6)-which were formed in the Precambrian anaerobic environment by the cyclization of squalene. Once molecular oxygen was in sufficient quantity in the atmosphere to permit squalene oxide genesis, a switching mechanism became operative to divert squalene from pentacyclic triterpenoid production to sterol synthesis (6, 7). The first compounds derived by the anaerobic cyclization of squalene oxide are the tetracyclic stereoisomers cycloartenol and lanosterol. Neither stereoisomer is known to be formed by cyclization in the same organism, whether the latter is a prokaryote or a eukaryote (2). This bifurcation in the sterol pathway is now recognized in biochemical textbooks (8-10) and in reviews on evolution (11-13) as a means to dissociate groups of organisms with an evolutionary history of oxygenic photosynthesis-e.g., as detected through the stereospecific formation of cycloartenol and its further metabolism of the 96,19-cyclopropyl ring-from those nonphotosynthetic progenitors and their descendants, which possess a lanosterolbased pathway (2). The association of the cycloartenol route and the endosymbiotic origin and subsequent loss of the chloroplast in some nonphotosynthetic systems is not clear. The biosynthesis of cycloartenol occurs in microsomes (14) and proceeds when the chloroplast is absent (15-18). In neither case is the biosynthesis of the stereoisomer influenced by the structure of the functional steroid at the end of the pathway, and their occurrence is not influenced by the molecular clock or mutatio...

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“…The acetylcholinesterase and (Na ÷ + K~)ATPase from rat erythrocytes and (Ca2~)ATPase from E. coli have different localization in the membrane, they have different dependence on the lipids for their enzymatic activity, and differ also in their metabolic function [4]. The membranes from rat erythrocytes and E. coli differ largely in properties, functions and composition, e.g., the bacterial membrane does not contain sterol whereas the erythrocyte membrane has one of the highest cholesterol/phospholipid ratios [34]. However, all the facts observed in rat erythrocyte and E. coli systems appear as a response to the general regulatory property of the T3 and T4 interplay on the membrane cooperative enzymes through changes in the membrane fluidity.…”

Section: Membrane Cooperative Enzymes and Thyroidmentioning

confidence: 99%