Evidence for a nonoxidative cyclization of squalene in the biosynthesis of tetrahymanol

Caspi, Eliahu; Zander, Jürgen; Greig, J. B.; Mallory, Frank B.; Conner, Robert L.; Landrey, Josephine R.

doi:10.1021/ja01015a048

Cited by 37 publications

(16 citation statements)

References 3 publications

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“…Of more crucial significance to our present discussion, is the fact that the sterol pathway in T. pyriformis has taken an alternative lane at the polyfurcation represented by the various modes of metabolism of squalene. Instead of proceeding to squalene oxide and then into the tetracyclic sterol series, squalene is protonated immediately and pentacyclized with an input of electrons by the inclusion of oxygen from water, which replaces the neutralization of the cation by deprotonation that occurs in sterol formation (66)(67)(68)(69). This remarkable process (Fig.…”

Section: The Membraneous Rolementioning

confidence: 99%

Role of sterols in membranes

Nes

1974

Lipids

263

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Sterols, or in rare cases structurally similar molecules, are biosynthesized or at least required by all eucaryotic organisms, as well as by many procaryotic ones, regardless of their status as plants, animals, or protista. This information, together with quantitative, structural, metabolic, and other data is reviewed. It is interpreted to mean that the primary role sterols play in nature is a nonmetabolic one as architectural components of membranes and that this role can be played, but less well, by other molecules which approximate the steroidal structure. The biosynthetic process should, therefore, and actually does not appear to be correlatable with this role, which, in turn, is correlatable with phylogenesis. The Δ24‐reduction‐alkylation bifurcation, for instance appears to be interrelated profoundly with the evolutionary differentiation of the animal from the plant kingdom.

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Section: The Membraneous Rolementioning

confidence: 99%

Role of sterols in membranes

Nes

1974

Lipids

263

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“…pation of cholest-5-ene in the biosynthesis of cholesterol would necessitate the postulation of a biogenetic route very different from that currently accepted (27). While non-oxidative cyclization pathways are known to exist in the case of lanosterol and the triterpene tetrahymanol (28,29), it would be difficult to account for the removal of the 4,4-dimethyl grouping in the absence of an oxygen function at C-3. We have found no evidence for the presence of lanostadiene in plaques.…”

Section: Discussionmentioning

confidence: 99%

Lipids of human atheroma VI. Hydrocarbons of the atheromatous plaque

Brooks

Steel

Harland

1970

Lipids

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“…This reaction was enhanced when some Oz was supplied, suggesting that molecular oxygen is required for sterol synthesis as generally accepted; there is an accumulation of evidence supporting the view that 2, 3-oxidosqualene is a common intermediate in the biosynthesis of sterols and triterpenes in various living organisms. Cyclization of squalene to form tetrahymanol in Tetrahymena is known to occur without using atmospheric oxygen (18)(19)(20), but sterol synthesis may be impossible in such a mechanism.…”

Section: Discussionmentioning

confidence: 99%

Metabolic Origin of Sterols in Rumen Protozoa

Hino

Kametaka

1978

J. Gen. Appl. Microbiol.

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Metabolic origin of sterols found in rumen protozoa was investigated by the use of 14C-labeled precursors. Hydrogenation of unsaturated sterols by protozoa was shown by incubation with 14C-cholesterol and 14C-13-sitosterol , suggesting that stigmastanol and campestanol in protozoa could be derived from exogenous C29 and C28 sterols, respectively. Low redox potential was found to be required for this hydrogenation reaction. No evidence was obtained for the assumption that protozoal cholestanol is formed by dealkylation of C(24)-alkyl-sterols. Incorporation of the label from 14C-acetate and 14C-mevalonate into the sterol fraction of protozoa was shown. Therefore, it appears highly probable that cholestanol is formed by de novo synthesis. The radioactivity in the protozoa! sterol fraction, however, was not high enough to conclude with definite certainty that rumen protozoa possess a sterol-synthesizing capacity; the possibility that contaminating organisms such as yeasts and fungi were responsible for the reaction could not be denied. Attempts to prove cholestanol synthesis by radio gas-liquid chromatography were unsuccessful due to low specific radioactivity of the protozoa! sterols labeled. Thus, poor or no capacity of rumen protozoa to synthesize sterols may, at least in part, explain the sterol requirement of these protozoa. In addition, other conversion and degradation reactions of sterols are described.In an earlier study it was found that the growth of rumen protozoa is stimulated by sterols (1). Then, it was thought that information on the fate of the sterols taken up might facilitate elucidation of the role of sterols in protozoa. Analysis of protozoa! sterols showed the presence of stigmastanol, campestanol, and cholestanol as the major sterols, together with their 5j9-forms and an unidentified sterol which was designated Compound X previously as the minor constituents (2). Clarification of the relationship between these and exogenous sterols should be the next step. It is readily assumed that stigmastanol was derived from exogenous 173

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Evidence for a nonoxidative cyclization of squalene in the biosynthesis of tetrahymanol

Cited by 37 publications

References 3 publications

Role of sterols in membranes

Role of sterols in membranes

Lipids of human atheroma VI. Hydrocarbons of the atheromatous plaque

Metabolic Origin of Sterols in Rumen Protozoa

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