scholarly journals The role of a cholesta-8,14-dien-3β-ol system in cholesterol biosynthesis

1969 ◽  
Vol 111 (5) ◽  
pp. 757-761 ◽  
Author(s):  
M. Akhtar ◽  
I. A. Watkinson ◽  
A. D. Rahimtula ◽  
D. C. Wilton ◽  
K. A. Munday
Keyword(s):  
Hydrogen Atom ◽  
Cholesterol Biosynthesis ◽  
Tritiated Water ◽  
Mevalonic Acid ◽  
Hydrogen Atoms ◽  
Steroid Biosynthesis ◽  
Methyl Group

The biosynthesis of cholesterol from squalene and tritiated water is described. Degradation of the cholesterol indicated that C-15 may be involved in cholesterol biosynthesis. In accordance with this view it is shown that in the conversion of [2RS−3H2]mevalonic acid into cholesterol one of the hydrogen atoms at C-15 is removed. A mechanism for the removal of the 14α-methyl group in steroid biosynthesis that involves the labilization of a C-15 hydrogen atom is outlined. In accordance with the requirement of this scheme it is shown that 4,4′-dimethyl-cholesta-8,14-dien-3β-ol is converted into cholesterol.

scholarly journals Incorporation of [2−14C,(5R)-5−3H1]mevalonic acid into cholesterol by a rat liver homogenate and into β-sitosterol and 28-isofucosterol by Larix decidua leaves

1969 ◽  
Vol 114 (4) ◽  
pp. 885-892 ◽  
Author(s):  
L J Goad ◽  
G. F. Gibbons ◽  
Loretta M. Bolger ◽  
H H Rees ◽  
T W Goodwin
Keyword(s):  
Double Bond ◽  
Hydrogen Atom ◽  
Rat Liver ◽  
Cholesterol Biosynthesis ◽  
Liver Homogenate ◽  
Mevalonic Acid ◽  
Atomic Ratio ◽  
Larix Decidua ◽  
Tritium Atom

1. Incubation of a rat liver homogenate with 3R-[2−14C,(5R)-5−3H1]mevalonic acid gave cholesterol with 3H/14C atomic ratio 6:5. 2. Conversion of the labelled cholesterol into 3β-acetoxy-6-nitrocholest-5-ene or cholest-4-ene-3,6-dione resulted in the loss of one tritium atom from C-6. 3. These results show that during cholesterol biosynthesis the 6α-hydrogen atom of a precursor sterol is eliminated during formation of the C-5–C-6 double bond. 4. Incorporation of 3R-[2−14C,(5R)-5−3H1]mevalonic acid into the sterols of larch (Larix decidua) leaves gave labelled cycloartenol and β-sitosterol with 3H/14C atomic ratios 6:6 and 6:5 respectively. 5. One tritium atom was lost from C-6 on conversion of the labelled β-sitosterol into either 3β-acetoxy-6-nitrostigmast-5-ene or stigmast-4-ene-3,6-dione, demonstrating that formation of the C-5–C-6 double bond of phytosterols also involves the elimination of the 6α-hydrogen atom of a precursor sterol. 6. The 3R-[2−14C,(5R)-5−3H1]mevalonic acid was also incorporated by larch (L. decidua) leaves into a sterol that co-chromatographed with 28-isofucosterol. Confirmation that the radioactivity was associated with 28-isofucosterol was obtained by co-crystallization with carrier 28-isofucosterol and ozonolysis of the acetate to give radioactively labelled 24-oxocholesteryl acetate. 7. The significance of these results to phytosterol biosynthesis is discussed.

Crystal Structure of Na9[H3W12O42]·24H2O, a Compound Containing the Protonated Paratungstate B Anion ('Acid Paratungstate'), and Cyclic Voltammetry of Acidified [H2W12O42]10- Solutions

1999 ◽  
Vol 52 (10) ◽  
pp. 955 ◽  
Author(s):  
Annette L. Nolan ◽  
Eric N. Wilkes ◽  
Trevor W. Hambley ◽  
Christine C. Allen ◽  
Robert C. Burns ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Cyclic Voltammetry ◽  
Hydrogen Atom ◽  
Internal Cavity ◽  
Molecular Orbital Calculations ◽  
Hydrogen Atoms ◽  
Triclinic Space Group ◽  
Electrochemically Active ◽  
Paratungstate B

Crystallization of a solid at pH 4.0 from an aqueous acidified Rh3+–[WO4]2− solution resulted in the isolation of Na9[H3W12O42]·24H 2 O, which contains the protonated paratungstate B anion and which is likely the species identified previously as ‘acid paratungstate’. The compound is triclinic, space group P1– , a 10.603(2), b 12.134(3), c 14.042(3) Å, α 114.78(1), β 101.84(1), γ 108.34(1)˚, V 1432.9(5) Å3 , Z 1, and the structure was solved to an R1 value of 0.0404 (wR 2 0.1108) for 5997 independent observed reflections. The anion exhibits essentially the same isopolytungstate framework as paratungstate B, [H2W12O42]10− , consisting of two W3O13 and two W3O14 structural subunits linked by shared vertices. Bond valence arguments place two of the hydrogen atoms unequivocally in the internal cavity of the anion, with the remaining hydrogen atom also likely located in this cavity, but disordered over several internal oxygen atoms. The protonation of [H2W12O42 ]10− is shown to lead to species that are electrochemically reducible. Extended-HÜckel molecular orbital calculations confirm that protonation of paratungstate B within the internal cavity leads to a change in composition of the LUMO, now based mainly on electrochemically reducible W3O13 as opposed to (essentially) non-reducible W3O14 structural subunits. This results in species that are considerably more electrochemically active than the unprotonated anion. The role of [H3W12O42]9− as an intermediate in the polymerization of [WO4]2− to give the solution form of ψ-metatungstate, [H7W11O40]7− , which crystallizes as [H4W11O38]6− , is also discussed.

scholarly journals Deuterium-labelled isotopomers of 2-C-methyl-d-erythritol as tools for the elucidation of the 2-C-methyl-d-erythritol 4-phosphate pathway for isoprenoid biosynthesis

2000 ◽  
Vol 346 (3) ◽  
pp. 737-742 ◽  
Author(s):  
Lionel CHARON ◽  
Jean-François HOEFFLER ◽  
Catherine PALE-GROSDEMANGE ◽  
Luisa-Maria LOIS ◽  
Narciso CAMPOS ◽  
...  
Keyword(s):  
Deuterium Atom ◽  
Mep Pathway ◽  
Significant Activity ◽  
Hydrogen Atoms ◽  
Methyl Group ◽  
E Coli ◽  
Dimethylallyl Diphosphate ◽  
Metabolic Route ◽  
Starter Unit

Escherichia coli synthesizes its isoprenoids via the mevalonate-independent 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway. The MC4100dxs::CAT strain, defective in deoxyxylulose-5-phosphate synthase, which is the first enzyme in this metabolic route, exclusively synthesizes its isoprenoids from exogenous 2-C-methyl-D-erythritol (ME) added to the culture medium. The fate of the hydrogen atoms in the MEP pathway was followed by the incorporation of [1,1-2H2]ME and [3,5,5,5-2H4]ME. The two C-1 hydrogen atoms of ME were found without any loss in the prenyl chain of menaquinone and/or ubiquinone on the carbon atoms derived from C-4 of isopentenyl diphosphate (IPP) and on the E-methyl group of dimethylallyl diphosphate (DMAPP), the C-5 hydrogen atoms on the methyl groups derived from IPP C-5 methyl group and the Z-methyl group of DMAPP. This showed that no changes in the oxidation state of these carbon atoms occurred in the reaction sequence between MEP and IPP. Furthermore, no deuterium scrambling was observed between the carbon atoms derived from C-4 and C-5 of IPP or DMAPP, suggesting a completely stereoselective IPP isomerase or no significant activity of this enzyme. The C-3 deuterium atom of [3,5,5,5-2H4]ME was preserved only in the DMAPP starter unit and was completely missing from all those derived from IPP. This finding, aided by the non-essential role of the IPP isomerase gene, suggests the presence in E. coli of two different routes towards IPP and DMAPP, starting from a common intermediate derived from MEP.

scholarly journals The formation and reduction of the 14,15-double bond in cholesterol biosynthesis

1971 ◽  
Vol 121 (1) ◽  
pp. 131-137 ◽  
Author(s):  
I. A. Watkinson ◽  
D. C. Wilton ◽  
K. A. Munday ◽  
M. Akhtar
Keyword(s):  
Double Bond ◽  
Hydrogen Atom ◽  
Rat Liver ◽  
Related Compound ◽  
Cholesterol Biosynthesis ◽  
Liver Homogenate ◽  
Compound Iiia ◽  
Sterol Biosynthesis ◽  
Methyl Group

It was shown that 100μg quantities of 4,4′-dimethyl[2-3H2]cholesta-8,14-dien-3β-ol (IIIa), tritiated cholesta-8,14-dien-3β-ol, 4,4′-dimethyl[2-3H2]cholesta-7,14-dien-3β-ol, dihydro[2-3H2]lanosterol and [24-3H]lanosterol were converted by a 10000g supernatant of rat liver homogenate into cholesterol in 17%, 54%, 6%, 9.5% and 24% yields respectively. From an incubation of dihydro[3α-3H]lanosterol with a rat liver homogenate in the presence of a trap up to 38% of the radioactivity was found to be associated with a fraction that was unambiguously shown to be 4,4′-dimethylcholesta-8,14-dien-3β-ol. Another related compound, 4,4′-dimethylcholesta-7,14-dien-3β-ol was also shown to be equally effective in its ability to trap compound (IIIa) from an incubation of dihydro[3α-3H]lanosterol. The mechanism of the further conversion of the compound (IIIa) into cholesterol occurred by the reduction of the 14,15-double bond and involved the addition of a hydrogen atom from the medium to C-15 and another from the 4-position of NADPH to C-14. Two possible mechanisms for the removal of the 14α-methyl group in sterol biosynthesis are discussed.

scholarly journals The biological conversion of 7-dehydrocholesterol into cholesterol and comments on the reduction of double bonds

1968 ◽  
Vol 106 (4) ◽  
pp. 803-810 ◽  
Author(s):  
D. C. Wilton ◽  
K A Munday ◽  
S. J. M. Skinner ◽  
M Akhtar
Keyword(s):  
Hydrogen Atom ◽  
Rat Liver ◽  
Enzyme System ◽  
Tritiated Water ◽  
Liver Homogenate ◽  
Double Bonds ◽  
Hydrogen Atoms ◽  
Biological Conversion ◽  
Microsomal Pellet

It is shown that the 7-dehydrocholesterol reductase-catalysed conversion of 7-dehydrocholesterol into cholesterol (II), with a 105000g microsomal pellet of rat liver in the presence of [4−3H2]NADPH, results in the transfer of radioactivity to the 7α-position of cholesterol. When the conversion is carried out in the presence of tritiated water the label is introduced exclusively at the 8β-position. However, when the conversion of 7-dehydrocholesterol into cholesterol is performed with a 500g supernatant of rat liver homogenate the radioactivity is incorporated at both the 7α- and the 8β-position. Evidence is provided for the presence of an enzyme system in the 500g supernatant that catalyses an equilibration of hydrogen atoms between those at the 4-position of NADPH and those of water. The work with stereospecifically labelled cofactors shows that both the equilibrating system and the 7-dehydrocholesterol reductase utilize the 4B-hydrogen atom of NADPH. In the light of these results a mechanism for the reduction of carbon–carbon double bonds is discussed.

Untersuchungen über Nebenreaktionen und den sterischen Verlauf bei der Direkt-Markierung einfacher Verbindungen mit Tritium-Gas

1968 ◽  
Vol 23 (6) ◽  
pp. 778-784
Author(s):  
Helmut Simon ◽  
Klaus Schmidt ◽  
Gerhard Müllhofer ◽  
Walter Eder ◽  
Ramiro Medina
Keyword(s):  
Hydrogen Atom ◽  
Tartaric Acid ◽  
Malic Acid ◽  
Glycolic Acid ◽  
Free Acid ◽  
Hydrogen Atoms ◽  
Methyl Group ◽  
Tartaric Acids ◽  
Carbon Carbon Bond ◽  
High Degree

Free tartaric acids, various tartrates, malic, hydroxymaleic, fumaric and aspartic acid, as well as propane diol-1.2 have been labelled by the Wilzbach method. In propane diol, hydrogen attached at C-2 is substituted by tritium three times faster than a hydrogen atom of the methyl group whereas that at C-l is substituted two times faster. Splitting of a carbon-carbon bond and fixation of tritium is eight to nine times more probable than the substitution of hydrogen by tritium. The OH group in propane diol as well as in tartaric and malic acid is more often replaced by atomic tritium than hydrogen atoms fixed at carbon. During the formation of malic acid from tartaric acid the second center of asymmetry is not attacked. The replacement of the OH group occurs in the cases of the free acid and the dimethylester to a high degree under inversion. Is the calcium or copper salt exposed retention prevails. In meso tartaric acid the carbon bound hydrogen is substituted with 12% inversion. When glycolic acid is formed from copper L-tartrate 29% inversion takes place.

scholarly journals The conformation of abscisic acid by n.m.r. and a revision of the proposed mechanism for cyclization during its biosynthesis

1984 ◽  
Vol 220 (1) ◽  
pp. 325-332 ◽  
Author(s):  
B V Milborrow
Keyword(s):  
Abscisic Acid ◽  
Hydrogen Atom ◽  
Pulse Sequence ◽  
Chair Conformation ◽  
Crystalline Form ◽  
Side Chain ◽  
Hydrogen Atoms ◽  
Methyl Group ◽  
Nuclear Overhauser Enhancement ◽  
Nuclear Overhauser

The n.m.r. spectrum of abscisic acid (ABA) formed from [1,2-13C2]acetate by the fungus Cercospora rosicola shows 13C-13C coupling between C-6′ (41.7 p.p.m.; 36 Hz) and the downfield 6′-methyl group (6′-Me) (24.3 p.p.m, 36 Hz). This 6′-Me, therefore, is derived from C-3′ of mevalonate [Bennett, Norman & Maier (1981) Phytochemistry 20, 2343-2344]. An i.n.e.p.t. (insensitive nuclei enhanced by polarization transfer) pulse sequence demonstrated that the downfield 13C signal is produced by the 6′-Me that gives rise to the upfield 1H 6′-Me signal (23.1 d). The absolute configuration of this, the equatorial 6′-Me group, was determined as 6′-pro-R by decoupling and n.O.e. (nuclear-Overhauser-enhancement) experiments at 300 MHz using ABA, ABA in which the axial 6′-pro-S 5′-hydrogen atom had been exchanged with 2H in NaO2H and the 1′,4′-cis- and 1′,4′-trans-diols formed from these samples. The configuration at C-1′ and at C-6′ are now compatible with a chair-folded intermediate during cyclization, as proposed for beta- and epsilon-rings of carotenoids. ABA in solution exists, as in the crystalline form, with the ring in a pseudo-chair conformation. The side chain is axial and the C-3 Me and the C-5 hydrogen atoms are predominantly cis(Z).

scholarly journals The incorporation of a hydrogen atom at C-15 of cholesterol biosynthesized from squalene

1969 ◽  
Vol 114 (4) ◽  
pp. 801-806 ◽  
Author(s):  
M Akhtar ◽  
A. D. Rahimtula ◽  
D. C. Wilton
Keyword(s):  
Hydrogen Atom ◽  
Cholesterol Biosynthesis ◽  
Tritiated Water ◽  
Total Radioactivity ◽  
Chemical Degradation

Cholesterol is biosynthesized from squalene in the presence of tritiated water. Chemical degradation reveals that a considerable percentage of the total radioactivity is present at C-15. This result confirms the previous observations on the involvement of a C-15 hydrogen atom in cholesterol biosynthesis.

Formation of surface layer of hydrogen in pure aluminum

2019 ◽  
Vol 484 (1) ◽  
pp. 56-60
Author(s):  
D. A. Indejtsev ◽  
E. V. Osipova
Keyword(s):  
Surface Layer ◽  
Hydrogen Atom ◽  
Ab Initio ◽  
Pure Aluminum ◽  
Hydrogen Atoms ◽  
Energy Characteristics ◽  
Aluminum Crystal

Hydrogen atom behavior in pure aluminum is described by ab initio modelling. All main energy characteristics of the system consisting of hydrogen atoms in a periodic aluminum crystal are found.

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