scholarly journals The conversion of cholest-7-en-3β-ol into cholesterol. General comments on the mechanism of the introduction of double bonds in enzymic reactions

1967 ◽  
Vol 105 (3) ◽  
pp. 1187-1194 ◽  
Author(s):  
S. Marsh Dewhurst ◽  
M Akhtar
Keyword(s):  
Double Bond ◽  
Hydrogen Atom ◽  
Experimental Evidence ◽  
Double Bonds ◽  
Anaerobic Conditions ◽  
Hydrogen Atoms ◽  
Aerobic Conditions ◽  
Metabolic Studies ◽  
Hypothetical Mechanism ◽  
Dehydration Mechanism

Convenient syntheses of 6β-tritiated Δ7-cholestenol and 3α-tritiated Δ7-cholestene-3β,5α-diol are described. It was shown that the conversion of 6β-tritiated Δ7-cholestenol into cholesterol is accompanied by the complete retention of label. It was unambiguously established that the overall reaction leading to the introduction of the double bond in the 5,6-position in cholesterol occurs via a cis-elimination involving the 5α- and 6α-hydrogen atoms and that during this process the 6β-hydrogen atom remains completely undisturbed. Metabolic studies with 3α-tritiated Δ7-cholestene-3β,5α-diol revealed that under anaerobic conditions the compound is not converted into cholesterol. This observation, coupled with the previous work of Slaytor & Bloch (1965), is interpreted to exclude a hydroxylation–dehydration mechanism for the origin of the 5,6-double bond in cholesterol. It was also shown that under aerobic conditions 3α-tritiated Δ7-cholestene-3β,5α-diol is efficiently converted into cholesterol and that this conversion occurs through the intermediacy of 7-dehydrocholesterol. Cumulative experimental evidence presented in this paper and elsewhere is used to suggest that the 5,6-double bond in cholesterol originates through an oxygen-dependent dehydrogenation process and a hypothetical mechanism for this and related reactions is outlined.

scholarly journals The mechanism of the elaboration of ring b in ergosterol biosynthesis

1968 ◽  
Vol 108 (4) ◽  
pp. 527-531 ◽  
Author(s):  
M Akhtar ◽  
M. A. Parvez
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Double Bond ◽  
Ergosterol Biosynthesis ◽  
Hydrogen Atoms ◽  
Aerobic Conditions ◽  
Whole Cells ◽  
Dehydration Mechanism ◽  
Dehydrogenation Mechanism

Methods for the preparation of [3α−3H]ergosta-7,22-dien-3β-ol (5,6-dihydro-ergosterol), [5,6−3H2]ergosta-7,22-dien-3β-ol and [3α−3H]ergosta-7,22-diene-3β,5α-diol are described. It is shown that 5,6-dihydro[3α−3H]ergosterol on incubation under aerobic conditions with whole cells of Saccharomyces cerevisiae LK2G12 is efficiently converted into ergosterol. Studies carried out with dihydro[5α,6α−3H2]-ergosterol demonstrate that the introduction of the 5,6-double bond in ergosterol biosynthesis is attended by an overall cis-elimination of two hydrogen atoms. To differentiate between a hydroxylation–dehydration mechanism and a dehydrogenation mechanism, the metabolism of [3α−3H]ergosta-7,22-diene-3β,5α-diol was studied. It was shown that this diol is converted into ergosterol only under aerobic conditions. It is therefore suggested that the introduction of the 5,6-double bond of ergosterol does not occur through a hydroxylation–dehydration mechanism.

Photolyse du butène-1 dans l'ultraviolet à vide

1973 ◽  
Vol 51 (17) ◽  
pp. 2853-2859 ◽  
Author(s):  
Guy J. Collin
Keyword(s):  
Double Bond ◽  
Hydrogen Atom ◽  
Kinetic Energy ◽  
Thermal Energy ◽  
Hydrogen Atoms ◽  
Excited Molecules

The vacuum u.v. photolysis of 1 -butene was studied in the 147–105 nm region. The main products formed from the fragmentation of excited molecules are allene, 1,3-and 1,2-butadienes, ethylene, and acetylene. The addition of a hydrogen atom to the double bond produces mainly secondary butyl radicals (91%) at 147 nm. At 123.6 nm, this proportion becomes 82%. Thus at shorter wavelengths (10 and 11.6–11.8 eV), hydrogen atoms are produced with a kinetic energy higher than the thermal energy.

Cis-trans Isomerization in Polyisoprenes. Part VII. Double Bond Movement During Isomerization of Natural Rubber and Related Olefins

1967 ◽  
Vol 40 (3) ◽  
pp. 921-927
Author(s):  
J. I. Cunneen ◽  
G. M. C. Higgins ◽  
R. A. Wilkes
Keyword(s):  
Double Bond ◽  
Sulfur Dioxide ◽  
Natural Rubber ◽  
Structural Modification ◽  
Anaerobic Conditions ◽  
Aerobic Conditions ◽  
Trans Isomerization ◽  
Acidic Compounds

Abstract When trans-3-methyl-2-pentene or trans-3-methyl-3-hexene is treated with butadiene sulfone, thiolbenzoic acid, and dibenzoyl disulfide under anaerobic conditions, the olefin undergoes only cis-trans isomerization. However, similar reactions in the presence of oxygen or peroxides also cause changes in the position of the double bond. The latter structural modification is probably caused by acidic compounds formed by oxidation of the isomerization reagents. With natural rubber the nonrubber substances prevent movement of the double bond, and cis-trans isomerization is the sole change, even when the reaction with sulfur dioxide is carried out under aerobic conditions.

scholarly journals Metabolic Studies of Testicular, Epididymal, and Ejaculated Spermatozoa of the Ram

1968 ◽  
Vol 21 (1) ◽  
pp. 111 ◽  
Author(s):  
RN Murdoch ◽  
IG White
Keyword(s):  
Anaerobic Conditions ◽  
Pasteur Effect ◽  
Aerobic Conditions ◽  
Metabolic Studies ◽  
Testicular Spermatozoa

When testicular spermatozoa were incubated with glucose under aerobic conditions a much smaller percentage of the substrate could be accounted for as lactate than was the case with epididymal or ejaculated spermatozoa. Testicular spermatozoa also displayed a greater Pasteur effect and under anaerobic conditions all three types of spermatozoa converted glucose almost quantitatively to lactate.

The kinetics of the interaction of atomic hydrogen with olefines. V. Results obtained for a further series of compounds

1950 ◽  
Vol 202 (1069) ◽  
pp. 181-202 ◽  
Keyword(s):  
Double Bond ◽  
Hydrogen Atom ◽  
Atomic Hydrogen ◽  
Methyl Radicals ◽  
Hydrogen Atoms ◽  
Alkyl Radicals ◽  
Kinetics Of ◽  
Interesting Generalization

In this paper the efficiency of interaction of a hydrogen atom with a series of olefines has been determined, the olefines being members of the series obtained by progressively replacing the hydrogen atoms of ethylene by methyl radicals. The interesting generalization which emerges from this is that the efficiency of interaction does not vary very much with the nature of the alkyl substituents in the molecule, and calculations involving the heats of addition of a hydrogen atom to a double bond confirm this generalization. The data presented here are discussed critically in relation to information available on the reaction of CCl 3 radicals with olefines and of alkyl radicals with olefines, complete general agreement being demonstrated.

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.

Hydrogen exchange and double bond formation in cholesterol biosynthesis

1972 ◽  
Vol 180 (1059) ◽  
pp. 147-165 ◽  
Keyword(s):  
Double Bond ◽  
Hydrogen Exchange ◽  
Present Report ◽  
Cholesterol Biosynthesis ◽  
Bond Formation ◽  
Biological Tissues ◽  
Double Bonds ◽  
Hydrogen Atoms ◽  
And Migration

The conversion of lanosterol║to cholesterol requires a considerable number of intermediary steps involving loss or uptake of hydrogen atoms and formation and migration of nuclear double bonds. Detailed discussions on the intermediary steps in cholesterol biosynthesis are reported in several reviews (Olson 1965; Frantz & Schroepfer 1967; Goad 1970). In the present report some mechanisms in the formation of cholesterol and its sterol precursors from lanosterol are discussed. The relation between in vitro and in vivo pathways of cholesterol biosynthesis and the composition and metabolism of sterols in biological tissues is underlined.

The Course of Autoöxidation Reactions in Polyisoprenes and Allied Compounds. XI. Double-Bond Movement during the Autoöxidation of a Monoölefin

1946 ◽  
Vol 19 (4) ◽  
pp. 1022-1028 ◽  
Author(s):  
E. Harold Farmer ◽  
Donald A. Sutton
Keyword(s):  
Reaction Mechanism ◽  
Double Bond ◽  
Molecular Oxygen ◽  
Double Bonds ◽  
Hydrogen Atoms ◽  
Methylene Groups

Abstract In an earlier part of this investigation it was shown that the autoöxidation of Δ1,4-diene8 and Δ1,4,7-, etc., polyene compounds produces peroxido derivatives containing conjugated units, and to explain the formation of the latter a reaction-mechanism was proposed which postulated the detachment of hydrogen atoms from the reactive methylene groups under the action of molecular oxygen, and subsequent rearrangement of the resonating radical residues before oxygen and, finally, hydrogen combine therewith to give hydroperoxides: (see PDF for diagram) It was recognized that, if this mechanism is valid for methylene-interrupted diene or polyene systems, it might reasonably be expected to apply also to the formation of hydroperoxides by the action of oxygen either on simple olefins or on polyolefins containing two or more methylene groups between the double bonds. To demonstrate successfully that even the simplest olefin system capable of hydroperoxidation can give both of the oxygenated forms (A) and (B):

The Reaction of Thiol Compounds with the Vitamin-K Dependent Clotting Factors

1969 ◽  
Vol 21 (03) ◽  
pp. 573-579 ◽  
Author(s):  
P Fantl
Keyword(s):  
Prothrombin Time ◽  
Vitamin K ◽  
Anaerobic Conditions ◽  
Clotting Factors ◽  
Thiol Compounds ◽  
Aerobic Conditions ◽  
One Stage ◽  
Factor Ii ◽  
Ph Dependent ◽  
The One

SummaryTreatment of human and dog oxalated plasma with 0.2 to 1.0 × 10−1 M 2.3-dithiopropanol (BAL) or dithiothreitol (DTT) at 2–4° C for 30 min results in the reduction of the vitamin-K dependent clotting factors II, VII, IX and X to the respective-SH derivatives. The reaction is pH dependent. Under aerobic conditions the delayed one stage prothrombin time can be partly reversed. Under anaerobic conditions a gradual prolongation of the one stage prothrombin time occurs without reversal.In very diluted plasma treated with the dithiols, prothrombin can be converted into thrombin if serum as source of active factors VII and X is added. In contrast SH factors VII, IX and X are inactive in the specific tests. Reoxidation to active factors II, VII, IX and X takes place during adsorption and elution of the SH derivatives. The experiments have indicated that not only factor II but also factors VII, IX and X have active-S-S-centres.

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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