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Rahier A. Deuterated delta 7-cholestenol analogues as mechanistic probes for wild-type and mutated delta 7-sterol-C5(6)-desaturase. Biochemistry 2001; 40:256-67. [PMID: 11141078 DOI: 10.1021/bi001696b] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Deuterium-labeled 5alpha-cholest-7-en-3beta-ol (1) bearing one or two deuteriums at the C-5alpha and (or) C-6alpha positions was synthesized in high isotopic and chiral purity. These compounds were used as substrates with the microsomal wild-type Zea mays and recombinant Arabidopsis thaliana Delta(7)-sterol-C5(6)-desaturases (5-DES) to probe directly the stereochemistry and the mechanism of the enzymatic reaction. Clearly, in the conversion of 1 by both 5-DESs, the 6alpha-hydrogen is removed. [6alpha-(2)H]-5alpha-Cholest-7-en-3beta-ol shows an intermolecular deuterium kinetic isotope effect (DKIE) on V and V/K, (D6)V = 2.6+/-0.3, (D6)V/K = 2.4+/-0.1; and (D6)V = 2.3 +/-0.3, (D6)V/K = 2.3+/-0.2 for the Zea mays and A. thaliana wild-type 5-DES, respectively. In contrast, negligible or minor isotope effects, (D5)V = 0.99+/-0.04, (D5)V/K = 0.91+/-0.08; and (D5)V = 0.93 +/-0.06, (D5)V/K = 0.96+/-0.04, respectively, were observed with [5alpha-(2)H]-cholest-7-en-3beta-ol. The observed pattern of isotope effects strongly suggests that the plant 5-DES initiates oxidation by cleavage of the chemically activated C6alpha-H bond, a step which appears to be partially rate-limiting in the desaturation process. Cleavage of the C5-H bond has a negligible isotope effect, indicating that the desaturation involves asynchronous scission of the two C-H bonds at C5 and C6. We showed previously [Taton, M., et al. (2000) Biochemistry 39, 701] that threonine 114 was not essential to maintaining desaturase activity, although V/K values for mutant T114I and T114S were respectively 10-fold lower and 4-fold higher than that of the native 5-DES. In this study, we combined variation in enzyme structure and DKIE studies and showed that (D6)V and (D6)V/K increased respectively to 3.8+/-0.3 and 3.8+/-0.4 in mutant T114I and decreased respectively to 1.6+/-0.4 and 1.7+/- 0.1 in mutant T114S. The data suggest that the conserved hydroxyl function at position 114 in the ERG3 family makes the abstraction of the 6alpha-hydrogen atom substantially less rate-limiting during the 5-DES reaction. Based on the data, a tentative mechanism for the desaturation of cholest-7-en-3beta-ol is proposed.
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Affiliation(s)
- A Rahier
- Département Isoprénoïdes, Institut de Biologie Moléculaire des Plantes, CNRS FRE 2161, 28 rue Goethe, 67083 Strasbourg Cédex, France.
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Affiliation(s)
- E I Mercer
- Department of Biochemistry, University of Wales, Aberystwyth, Dyfed, U.K
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Shimokawa O, Kato Y, Kawano K, Nakayama H. Accumulation of 14 alpha-methylergosta-8,24(28)-dien-3 beta,6 alpha-diol in 14 alpha-demethylation mutants of Candida albicans: genetic evidence for the involvement of 5-desaturase. BIOCHIMICA ET BIOPHYSICA ACTA 1989; 1003:15-9. [PMID: 2653443 DOI: 10.1016/0005-2760(89)90092-1] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
14 alpha-Demethylation mutants of the fungus Candida albicans have been shown to accumulate 14 alpha-methylergosta-8,24(28)-dien-3 beta,6 alpha-diol. A derivative from one of these mutants (KD4900) that does not form this 6 alpha-hydroxylated sterol but is still defective in 14 alpha-demethylation (KD4950) was obtained. Mutational restitution of 14 alpha-demethylation capacity to this derivative resulted in the formation of the 5,6-saturated sterol ergosta-7,22-dien-3 beta-ol as the major product, clearly indicating that 5-desaturase deficiency exists in this demethylation-proficient revertant (KD4952). This implies that its parent, KD4950, which has lost the ability to form the hydroxylated sterol, also is deficient in 5-desaturation. We infer from the results that 5-desaturase is responsible for the formation of the hydroxylated sterol. However, it is unclear whether the hydroxylation represents a genuine step of the normal 5-desaturation reaction.
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Affiliation(s)
- O Shimokawa
- Department of Microbiology, School of Dentistry, Kyushu University, Fukuoka, Japan
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Abstract
5,7-Cholestadien-3 beta-ol was transformed into 14 beta-cholesta-5,7-dien-3 beta-ol in six steps. The inversion of the stereochemistry at C-14 was obtained by a selective protection of the delta 5 and the elaboration of the delta 7 double bond.
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Affiliation(s)
- M Anastasia
- Dipartimento di Chimica e Biochimica Medica, Facoltà di Medicina e Chirurgia, Università di Milano, Italy
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Reddy VV, Caspi E. Cholesterol biosynthesis by rat liver microsomes: concerning C-5 double bond introduction. JOURNAL OF STEROID BIOCHEMISTRY 1977; 8:1037-45. [PMID: 916675 DOI: 10.1016/0022-4731(77)90204-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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Tavares IA, Munday KA, Wilton DC. The pathway for the conversion of dihydroagnosterol into cholesterol in rat liver. Biochem J 1977; 166:11-5. [PMID: 901410 PMCID: PMC1164950 DOI: 10.1042/bj1660011] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Dihydroagnosterol is demethylated by a rat liver homogenate to give 4,4'-dimethylcholesta 7,9-dienol and then cholesta-7,9-dienol. The cholesta-7,9-dienol is isomerized to cholesta-8,14-dienol, which is converted into cholesterol by the normal pathway.
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Sliwowski JK, Reddy VR, Caspi E. The in vivo biosynthesis of cholesterol from (3RS,2R) [2-14C,2-3H]mevalonic acid in the brains of rats on normal and protein deficient diets. The stereochemistry of tritium atoms at C-7 and C-15. J Neurochem 1977; 28:1311-6. [PMID: 874493 DOI: 10.1111/j.1471-4159.1977.tb12325.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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9
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Galli Kienle M, Anastasia M, Cighetti G, Manzocchi A, Galli G. Inversion of the unnatural cis C/D sterol ring junction of 5alpha, 14beta-cholest-7en-3beta-ol by rat-liver enzymes. EUROPEAN JOURNAL OF BIOCHEMISTRY 1977; 73:1-6. [PMID: 837931 DOI: 10.1111/j.1432-1033.1977.tb11285.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Labelled 5alpha, 14beta-cholest-7-en-3beta-ol with the 'unnatural' cis C/D ring junction was synthesized. Incubations of this sterol with rat liver homogenate under aerobic conditions gave radioactive 5alpha-cholest-7-en-3beta-ol, 5alpha-cholest-8(14)-en-3beta-ol andcholesterol indicating the presence of enzymes in the rat liver capable of inverting the C/D cis to a trans configuration. No radioactivity was found associated with added 14beta-cholesterol showing the specificity of the 14alpha configuration for the enzymic conversion of a sterol molecule into cholesterol.
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REDDY VVR, CASPI E. The Mechanism of C-5(6) Double Bond Introduction in the Biosynthesis of Cholesterol-by Rat Liver Microsomes. Consideration of a Mechanism Similar to the Oxidation of o-Diphenols. ACTA ACUST UNITED AC 1976. [DOI: 10.1111/j.1432-1033.1976.tb10943.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Alexander K, Akhtar M. The role of a 5alpha-hydroxylated intermediate in the formation of the 5, 6-double bond in cholesterol biosynthesis. Biochem J 1975; 145:345-52. [PMID: 1156363 PMCID: PMC1165223 DOI: 10.1042/bj1450345] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
If the biological conversion of cholest-7-en-3beta-ol (I) into cholesterol (IV) occurred thorugh the intermediacy of cholest-7-ene-3beta,5alpha-diol (II) then the factor(s) adversely affecting the convwesion of the 5alpha-hydroxy sterol (II) into cholesterol must at least equally adversely affect the formation of cholesterol from cholest-7-en-3beta-ol. By using partial denaturation techniquws and dual-labelled precursors it was shown that the enzyme system responsible for the conversion of the 5alpha-hydroxy sterol (II) into cholesterol denatured faster than that for the corresponding conversion from cholest-7-en-3beta-ol (I).
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Cook IF, Lloyd-Jones JG, Rees HH, Goodwin TW. The stereochemistry of hydrogen elimination from C-7 during biosynthesis of ecdysones in insects and plants. Biochem J 1973; 136:135-45. [PMID: 4772621 PMCID: PMC1165933 DOI: 10.1042/bj1360135] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
1. [7alpha-(3)H(1)]- and [7beta-(3)H(1)]-Cholesterol were synthesized by a modified method. 2. The stereochemistry of Delta(7)-bond formation during ecdysone and ecdysterone biosynthesis in the insect, Calliphora erythrocephala and the plants, Taxus baccata and Polypodium vulgare was investigated by using [4-(14)C,7alpha-(3)H(1)]cholesterol and [4-(14)C,7beta-(3)H(1)]cholesterol. 3. In each case, the 7beta hydrogen was stereospecifically eliminated. 4. The possible significance of the results is discussed in relation to double-bond formation in other systems and the stage at which the Delta(7) bond is introduced during ecdysone biosynthesis.
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The Fate of the 6α-Hydrogen of 5α-Cholest-7-en-3β-ol in the Conversion to 7-Dehydrocholesterol by Rat Liver Microsomes. J Biol Chem 1971. [DOI: 10.1016/s0021-9258(19)76985-3] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
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Wilton DC, Akhtar M. The stereochemistry of hydrogen elimination during 7,8-double bond formation by Tetrahymena pyriformis. Biochem J 1970; 116:337-9. [PMID: 5435681 PMCID: PMC1185370 DOI: 10.1042/bj1160337] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
It is shown that formation of the 7,8-double bond in the conversion of cholesterol into cholesta-5,7,22-trien-3beta-ol involves the removal of the 7beta- and 8beta-hydrogen atoms.
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Bimpson T, Goad LJ, Goodwin TW. The stereochemistry of hydrogen elimination at C-7,C-22 and C-23 during the conversion of cholesterol (cholest-5-en-3 beta-ol) into cholesta-5,7,22-trien-3 beta-ol by Tetrahymena pyriformis. Biochem J 1969; 115:857-8. [PMID: 5357026 PMCID: PMC1185216 DOI: 10.1042/bj1150857] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
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Goad LJ, Gibbons GF, Bolger LM, Rees HH, Goodwin TW. Incorporation of (2-14C, (5r)-5-3H1) mevalonic acid into cholesterol by a rat liver homogenate and into beta-sitosterol and 28-isofucosterol by larix decidua leaves. Biochem J 1969; 114:885-92. [PMID: 5348842 PMCID: PMC1184980 DOI: 10.1042/bj1140885] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
1. Incubation of a rat liver homogenate with 3R-[2-(14)C,(5R)-5-(3)H(1)]mevalonic acid gave cholesterol with (3)H/(14)C atomic ratio 6:5. 2. Conversion of the labelled cholesterol into 3beta-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 6alpha-hydrogen atom of a precursor sterol is eliminated during formation of the C-5-C-6 double bond. 4. Incorporation of 3R-[2-(14)C,(5R)-5-(3)H(1)]mevalonic acid into the sterols of larch (Larix decidua) leaves gave labelled cycloartenol and beta-sitosterol with (3)H/(14)C atomic ratios 6:6 and 6:5 respectively. 5. One tritium atom was lost from C-6 on conversion of the labelled beta-sitosterol into either 3beta-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 6alpha-hydrogen atom of a precursor sterol. 6. The 3R-[2-(14)C,(5R)-5-(3)H(1)]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.
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Akhtar M, Rahimtula AD, Wilton DC. The incorporation of a hydrogen atom at C-15 of cholesterol biosynthesized from squalene. Biochem J 1969; 114:801-6. [PMID: 5343788 PMCID: PMC1184967 DOI: 10.1042/bj1140801] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
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.
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Abstract
1. A convenient synthesis of 24-methylene[23,25-(3)H(3)]dihydrolanosterol is described. 2. A general anaerobic-aerobic method for the incorporation of sterols into whole yeast cells is also described and illustrated by experiments with (3)H-labelled lanosterol. 3. The method was used to convert labelled 24-methylene-dihydrolanosterol into ergosterol, in good yield, by Saccharomyces cerevisiae. 4. Degradation of the biosynthetic ergosterol provided confirmation of the conversion, which supports the proposed mechanism for the biosynthesis of the ergosterol side chain. 5. Mechanisms for the further conversion of the 24-methylene side chain into the ergosterol side chain are discussed and it was shown that a compound, [3alpha-(3)H(1)]-ergost-7-en-3beta-ol, with a fully saturated side chain, can also be efficiently incorporated into ergosterol. 6. This result was confirmed by a procedure involving formation of the 5,8-epidioxide and subsequently the 5,8-epidioxy-22,23-epoxide of the biosynthetic ergosterol.
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Rahimtula AD, Wilton DC, Akhtar M. The conversion of steroid 7,9-dienes into cholesterol. Biochem J 1969; 112:545-6. [PMID: 4308331 PMCID: PMC1187747 DOI: 10.1042/bj1120545] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
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Akhtar M, Watkinson IA, Rahimtula AD, Wilton DC, Munday KA. The role of a cholesta-8,14-dien-3-beta-ol system in cholesterol biosynthesis. Biochem J 1969; 111:757-61. [PMID: 5783476 PMCID: PMC1187605 DOI: 10.1042/bj1110757] [Citation(s) in RCA: 38] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
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-(3)H(2)]mevalonic acid into cholesterol one of the hydrogen atoms at C-15 is removed. A mechanism for the removal of the 14alpha-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-3beta-ol is converted into cholesterol.
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Scallen TJ, Schuster MW. A pyridine nucleotide requirement for the enzymatic conversion of delta-7-cholesten-3-beta-ol to 7-dehydrocholesterol. Steroids 1968; 12:683-7. [PMID: 4387235 DOI: 10.1016/s0039-128x(68)80022-4] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
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24
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Brodie HJ, Possanza G, Townsley JD. Studies on the mechanism of estrogen biosynthesis. V. Stereochemical comparison of aromatization in placental and microbiological systems. BIOCHIMICA ET BIOPHYSICA ACTA 1968; 152:770-7. [PMID: 4385516 DOI: 10.1016/0005-2760(68)90123-9] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
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25
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Abstract
Methods for the preparation of [3alpha-(3)H]ergosta-7,22-dien-3beta-ol (5,6-dihydro-ergosterol), [5,6-(3)H(2)]ergosta-7,22-dien-3beta-ol and [3alpha-(3)H]ergosta-7,22-diene-3beta,5alpha-diol are described. It is shown that 5,6-dihydro[3alpha-(3)H]ergosterol on incubation under aerobic conditions with whole cells of Saccharomyces cerevisiae LK(2)G(12) is efficiently converted into ergosterol. Studies carried out with dihydro[5alpha,6alpha-(3)H(2)]-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 [3alpha-(3)H]ergosta-7,22-diene-3beta,5alpha-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.
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Akhtar M, Parvez MA, Hunt PF. The introduction of the C-22-C-23 ethylenic linkage in ergosterol biosynthesis. Biochem J 1968; 106:623-6. [PMID: 5639918 PMCID: PMC1198551 DOI: 10.1042/bj1060623] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Methods for the chemical synthesis of [23-(3)H(2)]lanosterol, [23,25-(3)H(3)]24-methyldihydrolanosterol and [24,28-(3)H(2)]24-methyldihydrolanosterol are described. It is shown that, in the biosynthesis of ergosterol from [26,27-(14)C(2),23-(3)H(2)]lanosterol by the whole cells of Saccharomyces cerevisiae, one of the original C-23 hydrogen atoms is lost and the other is retained at C-23 of ergosterol. It is also shown that 24-methyldihydrolanosterol is converted into ergosterol in good yield and without prior conversion into a 24-methylene derivative. On the basis of these results possible pathways for the formation of the ergosterol side chain from a 24-methylene side chain are discussed.
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Wilton DC, Munday KA, Skinner SJ, Akhtar M. The biological conversion of 7-dehydrocholesterol into cholesterol and comments on the reduction of double bonds. Biochem J 1968; 106:803-10. [PMID: 4384136 PMCID: PMC1198583 DOI: 10.1042/bj1060803] [Citation(s) in RCA: 64] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
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-(3)H(2)]NADPH, results in the transfer of radioactivity to the 7alpha-position of cholesterol. When the conversion is carried out in the presence of tritiated water the label is introduced exclusively at the 8beta-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 7alpha- and the 8beta-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.
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