Cholesterol metabolism and vitamin B6. I. Hepatic cholesterogenesis and pyridoxine deficiency

1969 ◽  
Vol 47 (6) ◽  
pp. 631-635 ◽  
Author(s):  
P. J. Lupien ◽  
C. M. Hinse ◽  
M. Avery
Keyword(s):  
Rat Liver ◽  
High Speed ◽  
Cholesterol Metabolism ◽  
Reductase Activity ◽  
Liver Microsomes ◽  
Liver Homogenate ◽  
Supernatant Fraction ◽  
Liver Cholesterol ◽  
Pyridoxine Deficiency ◽  
Hepatic Cholesterogenesis

Hepatic cholesterogenesis was studied in pair-fed and pyridoxine-deficient rats as well as in rat liver homogenate systems. Crossover of various subcellular components from pair-fed homogenates into pyridoxine-deficient homogenate systems and vice versa was also done.On 8 weeks of pyridoxine deficiency, acetate-14C incorporation rates into liver cholesterol increased by a factor of approximately 10. The same phenomenon was observed with the total liver homogenate systems.Pyridoxine deficiency does not appear to affect HMG-CoA reductase activity of pyridoxine-deficient liver microsomes sufficiently to explain the rapid acetate-1-14C incorporation rates in this same tissue. The activating system(s) responsible for the 10-fold increase in acetate-14C incorporation rates into pyridoxine-deficient rat liver cholesterol appears to be located in the high-speed supernatant fraction. Other subcellular components such as lysosomes and mitochondria are probably implicated to some extent in this phenomenon. The results indicate that vitamin B6 is necessary for normal hepatic cholesterogenesis in the rat.The significance of these findings and the possible relationship between these factors are discussed.

Biosynthesis of 1,2-3H and 4-14C steroid sulfates of high specific activity

1970 ◽  
Vol 48 (1) ◽  
pp. 148-150 ◽  
Author(s):  
J. Torday ◽  
G. Hall ◽  
M. Schweitzer ◽  
C. J. P. Giroud
Keyword(s):  
Rat Liver ◽  
Specific Activity ◽  
Liver Homogenate ◽  
High Specific Activity ◽  
Supernatant Fraction ◽  
Metabolic Studies

A supernatant fraction of rat liver homogenate enriched with ATP was used for the biosynthesis of the ester sulfates of several 3H and 14C steroids of the pregn-4-ene series. The method provides a simple means to prepare steroid sulfates of high specific activity for use in either metabolic studies or as reference compounds in the quantification of such conjugates by isotope assays.

METHYLATION OF THE 3-OH POSITION OF CATECHOL ACIDS BY RAT LIVER AND KIDNEY PREPARATIONS

1958 ◽  
Vol 36 (5) ◽  
pp. 491-497 ◽  
Author(s):  
J. Pellerin ◽  
A. D'Iorio
Keyword(s):  
Enzymatic Activity ◽  
Rat Liver ◽  
Paper Chromatography ◽  
Reduced Glutathione ◽  
Liver Homogenate ◽  
Supernatant Fraction ◽  
Hydroxybenzoic Acid ◽  
Dihydroxybenzoic Acid ◽  
Kidney Homogenate ◽  
Liver And Kidney

3,4-Dihydroxybenzoic acid, 3,4-dihydroxyphenylacetic acid, 3,4-dihydroxymandelic acid, and 3,4-dihydroxycinnamic acid were separately incubated with L-methionine-methyl-C14 in the presence of rat liver or kidney homogenate. In each case, the radioactive metabolite separated by paper chromatography was found to have migrating properties similar to those of the 3-methoxy-4-hydroxyphenolic acid. This reaction was enhanced by the addition of ATP, Mg++, and reduced glutathione. When 3-hydroxybenzoic acid was incubated in this medium no methylated derivative was obtained. Preliminary experiments indicated that the enzymatic activity was contained mostly in the supernatant fraction. It was also noted that liver homogenate was much more active than kidney homogenate in methylating catechol acids.

In Vivo and in Vitro Studies on the Regulatory Link between 3-Hydroxy-3- methylglutaryl Coenzyme A Reductase and Cholesterol 7α-Hydroxylase in Rat Liver

1999 ◽  
Vol 54 (5-6) ◽  
pp. 371-382 ◽  
Author(s):  
Meinrad Boll ◽  
Lutz W. D. Weber ◽  
Juliana Plana ◽  
Andreas Stampfl
Keyword(s):  
Bile Acid ◽  
Rat Liver ◽  
Cholesterol Metabolism ◽  
Ex Vivo ◽  
Reductase Activity ◽  
Cholesterol Biosynthesis ◽  
In Vitro Studies ◽  
High Cholesterol Diet ◽  
Hmgcoa Reductase

Abstract The activities of 3-hydroxy-3-methylglutaryl CoA reductase (HMGCoA reductase; EC 1.1.1.34), rate-limiting enzyme of cholesterol biosynthesis, and cholesterol 7α-hydroxylase (EC 1.14.13.17), key enzyme of the neutral bile acid synthesis pathway, were measured in the microsomal fraction of rat liver and in rat liver cells to investigate the coordinate regulation of the two pathways. Both enzyme activities exhibited the same diurnal rhythm and responded in a coordinate fashion to fasting or bile acid-feeding (decrease) and to cholestyramine-feeding (increase). Cholesterol-feeding decreased the activity of HMGCoA reductase, increased that of cholesterol 7α-hydroxylase, and concomitantly increased free cholesterol in microsomes. In an ex vivo setting using primary hepatocytes from animals fed a high cholesterol diet the activity of HMGCoA reductase was initially low and that of cholesterol 7α-hydroxylase was elevated. Release of cholesterol into the medium with ongoing incubation caused HMGCoA reductase activity to increase, and that of cholesterol 7α-hydroxylase to decline. Incubation of hepatocytes with a cholesterol-containing lipoprotein fraction stimulated the activity of cholesterol 7α-hydroxylase, but left HMGCoA reductase activity unaffected. The results confirm the idea of a joint regulation of the two key enzymes of cholesterol metabolism in response to the levels of substrate and metabolites, and support the notion that with respect to bile acid and cholesterol levels, respectively, regulation of HMGCoA reductase activity may be secondary to that of cholesterol 7α-hydroxylase. The in vitro studies supply evidence that the effects of cholesterol and bile acid excess or deficiency are direct and do not involve accessory changes of hormone levels or mediators.

scholarly journals The function of subcellular fractions in the oxidation of glutathione in rat liver homogenate

1970 ◽  
Vol 117 (5) ◽  
pp. 951-956 ◽  
Author(s):  
P. C. Jocelyn
Keyword(s):  
Uric Acid ◽  
Xanthine Oxidase ◽  
Rat Liver ◽  
Liver Homogenate ◽  
No Oxidation ◽  
Urate Oxidase ◽  
Supernatant Fraction ◽  
Endogenous Substrate ◽  
Additional Protein ◽  
Microsome Fraction

1. The aerobic loss of GSH added to the supernatant fraction from rat liver is much increased by including the microsome fraction, which both inhibits the concurrent reduction of the GSSG formed and also augments the net oxidation rate. 2. Oxidation occurs with a mixture of dialysed supernatant and a protein-free filtrate; the latter is replaceable by hypoxanthine and the former by xanthine oxidase, whereas fractions lacking this enzyme give no oxidation. 3. In all these instances augmentation occurs with microsomes, with fractions having urate oxidase activity and with the purified enzyme; uric acid and microsomes alone also support the oxidation. 4. Evidence implicating additional protein factors is discussed. 5. It is suggested that GSH oxidation by homogenate is linked through glutathione peroxidase to the reaction of endogenous substrate with supernatant xanthine oxidase and of the uric acid formed with peroxisomal urate oxidase.

scholarly journals Inhibition of microsomal lipid peroxidation by glutathione and glutathione transferases B and AA. Role of endogenous phospholipase A2

1984 ◽  
Vol 220 (1) ◽  
pp. 243-252 ◽  
Author(s):  
K H Tan ◽  
D J Meyer ◽  
J Belin ◽  
B Ketterer
Keyword(s):  
Lipid Peroxidation ◽  
Phospholipase A2 ◽  
Rat Liver ◽  
Inhibitory Activity ◽  
Liver Microsomes ◽  
Supernatant Fraction ◽  
Rat Liver Microsomes ◽  
Microsomal Lipid Peroxidation ◽  
Soluble Supernatant

Lipid peroxidation in vitro in rat liver microsomes (microsomal fractions) initiated by ADP-Fe3+ and NADPH was inhibited by the rat liver soluble supernatant fraction. When this fraction was subjected to frontal-elution chromatography, most, if not all, of its inhibitory activity could be accounted for by the combined effects of two fractions, one containing Se-dependent glutathione (GSH) peroxidase activity and the other the GSH transferases. In the latter fraction, GSH transferases B and AA, but not GSH transferases A and C, possessed inhibitory activity. GSH transferase B replaced the soluble supernatant fraction as an effective inhibitor of lipid peroxidation in vitro. If the microsomes were pretreated with the phospholipase A2 inhibitor p-bromophenacyl bromide, neither the soluble supernatant fraction nor GSH transferase B inhibited lipid peroxidation in vitro. Similarly, if all microsomal enzymes were heat-inactivated and lipid peroxidation was initiated with FeCl3/sodium ascorbate neither the soluble supernatant fraction nor GSH transferase B caused inhibition, but in both cases inhibition could be restored by the addition of porcine pancreatic phospholipase A2 to the incubation. It is concluded that the inhibition of microsomal lipid peroxidation in vitro requires the consecutive action of phospholipase A2, which releases fatty acyl hydroperoxides from peroxidized phospholipids, and GSH peroxidases, which reduce them. The GSH peroxidases involved are the Se-dependent GSH peroxidase and the Se-independent GSH peroxidases GSH transferases B and AA.

scholarly journals Methane production by the membranous fraction of Methanobacterium thermoautotrophicum

1980 ◽  
Vol 190 (1) ◽  
pp. 177-182 ◽  
Author(s):  
F D Sauer ◽  
J D Erfle ◽  
S Mahadevan
Keyword(s):  
Methane Production ◽  
High Speed ◽  
High Pressures ◽  
Reductase Activity ◽  
Membrane Vesicles ◽  
Methanobacterium Thermoautotrophicum ◽  
Cell Extract ◽  
Supernatant Fraction ◽  
Coenzyme M ◽  
Intact Membrane

Intact membrane vesicles are required to synthesize methane from CO2 and H2 by disrupted preparations of Methanobacterium thermoautotrophicum cells. When membrane vesicles were removed by high-speed centrifugation at 226 600 g, the remaining supernatant fraction no longer synthesized methane. Alternatively, if vesicle structure was disrupted by passage through a Ribi cell fractionator at very high pressures (345 MPa), the bacterial cell extract, with all the particulate fraction in it, did not synthesize methane. Methyl-coenzyme M, a new coenzyme first described by McBride & Wolfe [(1971) Biochemistry 10, 2317–2324], was shown to stimulate methane production from CO2 and H2, as previously reported, but the methyl group of the coenzyme did not appear to be a precursor of methane in this reaction. No methyl-coenzyme M reductase activity was detected in the cytoplasmic fraction of M. thermoautotrophicum cells.

scholarly journals Separation and characterization of the aldehydic products of lipid peroxidation stimulated by ADP-Fe2+ in rat liver microsomes

1982 ◽  
Vol 208 (1) ◽  
pp. 129-140 ◽  
Author(s):  
H Esterbauer ◽  
K H Cheeseman ◽  
M U Dianzani ◽  
G Poli ◽  
T F Slater
Keyword(s):  
Lipid Peroxidation ◽  
Rat Liver ◽  
Liver Microsomes ◽  
Thiobarbituric Acid ◽  
Polar Fraction ◽  
Supernatant Fraction ◽  
Major Type ◽  
Rat Liver Microsomes ◽  
Acid Reaction ◽  
The Individual

1. Methods using t.l.c. and high-pressure liquid chromatography (h.p.l.c.) have been used to separate the complex variety of substances possessing a carbonyl function that are produced during lipid peroxidation. 2. The major type of lipid peroxidation studied was the ADP-Fe2+-stimulated peroxidation of rat liver microsomal phospholipids. Preliminary separation of the polar and non-polar products was achieved by t.l.c.: further separation and identification of individual components was performed by h.p.l.c. Estimations were performed on microsomal pellets and the supernatant mixture after incubation of microsomes for 30 min at 37 degrees C. 3. The polar fraction was larger than the non-polar fraction when expressed as nmol of carbonyl groups/g of liver. In the non-polar supernatant fraction the major contributors were n-alkanals (31% of the total), alpha-dicarbonyl compounds (22%) and 4-hydroxyalkenals (37%) with the extraction method used. 4. Major individual contributors to the non-polar fraction were found to be propanal, 4-hydroxynonenal, hexanal and oct-2-enal. Other components identified include butanal, pent-2-enal, hex-2-enal, hept-2-enal, 4-hydroxyoctenal and 4-hydroxyundecenal. The polar carbonyl fraction was less complex than the non-polar fraction, although the identities of the individual components have not yet been established. 5. Since these carbonyl compounds do not react significantly in the thiobarbituric acid reaction, which largely demonstrates the presence of malonaldehyde, it is concluded that considerable amounts of biologically reactive carbonyl derivatives are released in lipid peroxidation and yet may not be picked up by the thiobarbituric acid reaction.

Cytochrome b5/Cytochrome b5 Reductase Complex in Rat Liver Microsomes has NADH-Linked Aquacobalamin Reductase Activity

1992 ◽  
Vol 122 (4) ◽  
pp. 940-944 ◽  
Author(s):  
Fumio Watanabe ◽  
Yoshihisa Nakano ◽  
Hisako Saido ◽  
Yoshiyuki Tamura ◽  
Hiroyuki Yamanaka
Keyword(s):  
Rat Liver ◽  
Reductase Activity ◽  
Cytochrome B5 ◽  
Liver Microsomes ◽  
Rat Liver Microsomes ◽  
Cytochrome B5 Reductase
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