scholarly journals Studies in phytosterol biosynthesis. Mechanism of biosynthesis of cycloartenol

1968 ◽  
Vol 107 (3) ◽  
pp. 417-426 ◽  
Author(s):  
H H Rees ◽  
L J Goad ◽  
T W Goodwin
Keyword(s):  
Solanum Tuberosum ◽  
Hydrogen Atom ◽  
Mevalonic Acid ◽  
Atomic Ratio ◽  
Side Chain ◽  
Hydrogen Migration ◽  
Biosynthetic Precursor

1. The mechanism of cycloartenol biosynthesis in leaves of Solanum tuberosum was investigated with the use of [2−14C,(4R)-4−3H1]mevalonic acid. 2. The 3H/14C atomic ratio in cycloartenol was 6:6, the same as that in squalene; this eliminates lanosterol as a possible biosynthetic precursor of cycloartenol, and indicates that a hydrogen migration from C-9 to C-8 occurs. 3. Chemical isomerization of the cycloartenol to lanosterol (3H/14C ratio 5:6) and parkeol (3H/14C ratio 6:6) confirms the hydrogen migration from C-9 to C-8. 4. Possible mechanisms for the biosynthesis of cycloartenol and parkeol are discussed. 5. The 3H/14C ratio for 24-methylenecycloartanol was 6:6, demonstrating that the hydrogen atom at C-24 is retained during alkylation of the cycloartenol side chain.

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.

scholarly journals Incorporation of dl-[2−14C]mevalonic acid lactone into β-carotene and the phytol side chain of chlorophyll in cotyledons of four species of pine seedlings

1967 ◽  
Vol 105 (1) ◽  
pp. 89-92 ◽  
Author(s):  
S. Wieckowski ◽  
T W Goodwin
Keyword(s):  
Mevalonic Acid ◽  
Side Chain ◽  
Pinus Silvestris ◽  
Pine Seedlings ◽  
Acid Lactone ◽  
Β Carotene

1. The incorporation of dl-[2−14C]mevalonic acid lactone into β-carotene and the phytol side chain of chlorophyll has been investigated in cotyledons of four species of pine seedlings (Pinus silvestris, P. contorta, P. radiata and P. jeffrei) grown in darkness and in light. 2. The relative incorporation of label into β-carotene and the phytol side chain of chlorophyll is similar to that observed in experiments on monocotyledons and dicotyledons. 3. The relative incorporation of 14CO2 into β-carotene and phytol is much higher than the incorporation of [2−14C]mevalonic acid.

Imaging intramolecular hydrogen migration with time- and momentum-resolved photoelectron diffraction

2021 ◽  
Author(s):  
Fukiko Ota ◽  
Shigeru Abe ◽  
Keisuke Hatada ◽  
Kiyoshi Ueda ◽  
Sergio Díaz-Tendero ◽  
...  
Keyword(s):  
Hydrogen Atom ◽  
Cross Section ◽  
Time Resolution ◽  
Ultrafast Spectroscopy ◽  
Scattering Cross Section ◽  
Photoelectron Diffraction ◽  
Hydrogen Migration ◽  
Scattering Cross ◽  
Intramolecular Hydrogen

Imaging ultrafast hydrogen migration with few- or sub-femtosecond time resolution is a challenge for ultrafast spectroscopy due to the lightness and small scattering cross section of the moving hydrogen atom....

BIOSYNTHESIS OF C19 STEROIDS FROM 4-14C-CHOLESTEROL AND 7-3H-PREGNENOLONE IN VIVO: CONSIDERATION OF NEW PATHWAYS

1962 ◽  
Vol 40 (2) ◽  
pp. 188-202 ◽  
Author(s):  
Shlomo Burstein ◽  
Ralph I. Dorfman
Keyword(s):  
Adrenal Adenoma ◽  
Mevalonic Acid ◽  
Compartment Model ◽  
Side Chain ◽  
Partition Chromatography ◽  
Steroid Nucleus ◽  
Single Intravenous Injection ◽  
Two Compartment Model ◽  
Specific Activities

ABSTRACT 3H and 14C specific activities of dehydroepiandrosterone, androsterone, 3α-hydroxy-5β-androstan-17-one and 3α-hydroxy-5α-androst-16-ene (without dilution) have been determined following a single intravenous injection of 4-14C-cholesterol and 7α-3H-pregnenolone to a virilized woman with an adrenal adenoma and massive dehydroepiandrosterone excretion. Assuming a one compartment model, or a two compartment model in which the injected radioactivity enters the compartment in which the precursor is secreted exclusively, a new pathway by which dehydroepiandrosterone is formed from cholesterol not through pregnenolone and possibly by cleavage of the side chain C-17 and C-20 is indicated. Analysis of the data by a model in which pregnenolone is secreted into two separate compartments in which progesterone and dehydroepiandrosterone are made, respectively, would explain the findings without necessitating the assumption of a new pathway. 3α-Hydroxy-5α-androst-16-ene was isolated from urine following incubation with β-glucuronidase and partition chromatography on celite suggesting that this steroid is a genuine natural product as surmised by Prelog & Ruzicka (1944) and Brooksbank & Haslewood (1950). 2-14C-Mevalonate was shown to give rise to C19 steroids which is the first in vivo demonstration that mevalonic acid is a precursor of the steroid nucleus in man.

Asparagine and glutamine: using hydrogen atom contacts in the choice of side-chain amide orientation 1 1Edited by J. Thornton

1999 ◽  
Vol 285 (4) ◽  
pp. 1735-1747 ◽  
Author(s):  
J.Michael Word ◽  
Simon C. Lovell ◽  
Jane S. Richardson ◽  
David C. Richardson
Keyword(s):  
Hydrogen Atom ◽  
Side Chain

Nonenzymatic Transformation of Riboflavin into 5,6-Dimethylbenzimidazole

1977 ◽  
Vol 32 (7-8) ◽  
pp. 523-527 ◽  
Author(s):  
Paul Renz ◽  
Rainer Wurm ◽  
Joachim Hörig
Keyword(s):  
Carboxylic Acid ◽  
Specific Radioactivity ◽  
Oxidative Degradation ◽  
Side Chain ◽  
Vitamin B ◽  
Enzymatic Process ◽  
Biosynthetic Precursor ◽  
Alkaline Conditions ◽  
Imidazoline Derivative

Riboflavin, the biosynthetic precursor of the 5,6-dimethylbenzimidazole moiety of vitamin B12, is transformed non-enzymatically into 5,6-dimethylbenzimidazole in small yield on treatment with 1 ɴ or 5 ɴ NaOH at 100 °C. Besides 5,6-dimethylbenzimidazole 1,2-diamino-4,5-dimethylbenzene, 1.2- dihydro-6,7-dimethyl-2-keto-1-ᴅ-ribityl-3-quinoxaline carboxylic acid and N-1-ᴅ-ribitylamino-2- amino-4,5-dimethylbenzene can be detected. When [1′-14C] riboflavin is used the 5,6-dimethyl­benzimidazole contains about 75 per cent of the specific radioactivity of riboflavin. N-1-ᴅ-ribityl- amino-2-amino-4,5-dimethylbenzene is transformed into 5,6-dimethylbenzimidazole more efficiently than riboflavin. Oxygen enhances the yield of 5,6-dimethylbenzimidazole and 1,2-diamino-4,5-di- methylbenzene from riboflavin as well as from N-1-ᴅ-ribitylamino-2-amino-4,5-dimethylbenzene. 1.2- diamino-4,5-dimethylbenzene reacts together with formaldehyde but not with formate to form 5,6-dimethylbenzimidazole under alkaline conditions at 100 °C. It is therefore suggested that the nonenzymatic reaction of riboflavin proceeds via N-1-ᴅ-ribityl- amino-2-amino-4,5-dimethylbenzene and 1,2-diamino-4,5-dimethylbenzene, and that the latter reacts with formaldehyde preferably formed by oxidative degradation of C-1′ of the ribityl side chain to form 5,6-dimethylbenzimidazole via its unstable imidazoline derivative. The possible relevance of these results for the enzymatic process is discussed.

scholarly journals Incorporation of [2−14C]mevalonic acid into phytoene by isolated chloroplasts

1967 ◽  
Vol 105 (1) ◽  
pp. 205-212 ◽  
Author(s):  
Josephine M. Charlton ◽  
K J. Treharne ◽  
T W Goodwin
Keyword(s):  
Ultrasonic Treatment ◽  
Magnesium Chloride ◽  
Mevalonic Acid ◽  
Side Chain ◽  
Isolated Chloroplasts

1. Chloroplasts prepared by the non-aqueous technique will, after fragmentation by ultrasonic treatment, incorporate [2−14C]mevalonic acid into phytoene, the first C40 compound formed in the biosynthetic sequence to coloured carotenoids. 2. With suspensions containing 3·5mg. of chlorophyll, the optimum amounts of cofactor required were ATP (10μmoles), magnesium chloride (20μmoles) and glutathione (20μmoles); neither NAD+ nor NADP+ was required. 3. Very small amounts of squalene are also formed and synthesis is stimulated by addition of NADH or NADPH. Phytoene synthesis was not affected by the presence of these cofactors and no lycopersene (the C40 homologue of squalene) was detected. 4. The phytol side chain of chlorophyll is also labelled under these conditions. 5. Preparations of developing chloroplasts are more active than preparations of mature chloroplasts.

Sign in / Sign up

Export Citation Format

Share Document