Distribution and oxidation of malondialdehyde in mice

The metabolism of melondialdehyde (MDA) by male and female Swiss mice was investigated. Distribution of an i.p. dose of MDA is rapid and uniform throughout the body. Conversion of ¹⁴C-labeled MDA to CO₂ is complete 4 hours after an i.p. dose of 5 μmol to 200 μmol with no signs of short term toxicity. The yields of CO₂ from [1-¹⁴C]-β-alanine, [3-¹⁴C]-β-alanine, [1-¹⁴C]-sodium acetate, and [2-¹⁴C]-sodium acetate were also determined. Comparison of the yields of CO₂ from this series of compounds suggests the intermediacy of malonic semialdehyde in the metabolism of MDA. High doses (600 μmol) of β-alanine or acetate given prior to ¹⁴C-MDA reduced the yield of ¹⁴CO₂. Ethanol and disulfiram were both inhibitors of MDA metabolism, indicating the involvement of aldehyde dehydrogenase in the oxidation of MDA.These data demonstrate the ability of animal tissues to rapidly remove exogeneously administered MDA. They also have implications with respect to the possible pathological consequences of MDA generation.     

Gluconate metabolism in germinated spores of Bacillus megaterium QM B1551: primary roles of gluconokinase and the pentose cycle

The metabolic pathway of gluconate, a major product of glucose metabolism during spore germination, was investigated in Bacillus megaterium QM B1551. Compared to the parent, mutant spores lacking gluconokinase could not metabolize gluconate, whereas the revertant simultaneously restored the enzyme activity and the ability to metabolize it, indicating that gluconokinase was solely responsible for the onset of gluconate metabolism. To identify a further metabolic route for gluconate, we determined 14C yields in acetate and CO2 formed from [14C]gluconate, and found that experimental ratios of 14CO2/[14C]acetate obtained from [2-14C]gluconate and [3,4-14C]gluconate were not compatible with the ratios predicted from the Entner-Doudoroff pathway. In contrast, when CO2 release caused by recycling (approx. 30%) was corrected, the ratios almost agreed with those from the pentose cycle. Comparison of specific radioactivities in acetate also supported the conclusion that gluconate was metabolized via the pentose cycle, subsequently metabolized via the Embden-Meyerhof pathway, and finally degraded to acetate and CO2 without a contribution by the Krebs cycle.     

Anaerobic metabolism of immediate methane precursors in Lake Mendota.

Lake Mendota sediments and the immediate overlying water column were studied to better understand the metabolism of the methanogenic precursors H2/CO2 and acetate in nature. The pool size of acetate (3.5 microns M) was very small, and the acetate turnover time (0.22h) was very rapid. The dissolved inorganic carbon pool was shown to be large (6.4 to 8.3 mM), and the turnover time was slow (111 H.). CO2 was shown to account for 41 +/- 5.5% of the methane produced in sediment. Acetate and H2/CO2 were simultaneously converted to CH4. The addition of H2 to sediments resulted in an increase specific activity of CH4 from H(14)CO3- and a decrease in specific activity of CH4 from [2-14C]acetate. Acetate addition resulted in a decrease in specific activity of CH4 from H(14)CO3-. The metabolism of H(14)CO3- or [2-14C]acetate to 14CH4 was not inhibited by addition of acetate or H2. After greater than 99% of added [2-14C]acetate had been turned over, 42% of the label was recovered as 14CH4 20% was recovered as 14CO2 and 38% was incorporated into sediment. Inhibitor studies of [2-14C]acetate metabolism in sediments demonstrated that CHCl3 completely inhibited CH4 formation, but not CO2 production. Air and nitrate addition inhibited CH4 formation and stimulated CO2 production, whereas fluoroacetate addition totally inhibited acetate metabolism. The oxidation of [2-14C]acetate to 14CO2 was shown to decrease with time when sediment was incubated before the addition of label, suggesting depletion of low levels of an endogenous sediment electron acceptor. Acetate metabolism varied seasonally and was related to the concentration of sulfate in the lake and interstitial water. Methanogenesis occurred in the sediment and in the water immediately overlying the sediment during period of lake stratification and several centimeters below the sediment-water interface during lake turnovers. These data indicate that methanogenesis in Lake Mendota sediments was limited by "immediate" methane precursor availability (i.e., acetate and H2), by competition for these substrates by nonmethanogens, and by seasonal variations which altered sediment and water chemistry.     

Anaerobic metabolism of immediate methane precursors in Lake Mendota.

Lake Mendota sediments and the immediate overlying water column were studied to better understand the metabolism of the methanogenic precursors H2/CO2 and acetate in nature. The pool size of acetate (3.5 microns M) was very small, and the acetate turnover time (0.22h) was very rapid. The dissolved inorganic carbon pool was shown to be large (6.4 to 8.3 mM), and the turnover time was slow (111 H.). CO2 was shown to account for 41 +/- 5.5% of the methane produced in sediment. Acetate and H2/CO2 were simultaneously converted to CH4. The addition of H2 to sediments resulted in an increase specific activity of CH4 from H(14)CO3- and a decrease in specific activity of CH4 from [2-14C]acetate. Acetate addition resulted in a decrease in specific activity of CH4 from H(14)CO3-. The metabolism of H(14)CO3- or [2-14C]acetate to 14CH4 was not inhibited by addition of acetate or H2. After greater than 99% of added [2-14C]acetate had been turned over, 42% of the label was recovered as 14CH4 20% was recovered as 14CO2 and 38% was incorporated into sediment. Inhibitor studies of [2-14C]acetate metabolism in sediments demonstrated that CHCl3 completely inhibited CH4 formation, but not CO2 production. Air and nitrate addition inhibited CH4 formation and stimulated CO2 production, whereas fluoroacetate addition totally inhibited acetate metabolism. The oxidation of [2-14C]acetate to 14CO2 was shown to decrease with time when sediment was incubated before the addition of label, suggesting depletion of low levels of an endogenous sediment electron acceptor. Acetate metabolism varied seasonally and was related to the concentration of sulfate in the lake and interstitial water. Methanogenesis occurred in the sediment and in the water immediately overlying the sediment during period of lake stratification and several centimeters below the sediment-water interface during lake turnovers. These data indicate that methanogenesis in Lake Mendota sediments was limited by "immediate" methane precursor availability (i.e., acetate and H2), by competition for these substrates by nonmethanogens, and by seasonal variations which altered sediment and water chemistry.     

Metabolism of glucose into glutamate via the hexose monophosphate shunt and its inhibition by 6-aminonicotinamide in rat brain in vivo

The treatment of rats for 4 h with 6-aminonicotinamide (60 mg kg-1) resulted in an 180-fold increase in the concentration of 6-phosphogluconate in their brains; glucose increased 2.6-fold and glucose 6-phosphate, 1.7-fold. Moreover, lactate decreased by 20%, glutamate by 8% and gamma-aminobutyrate by 12%, and aspartate increased by 10%. No significant changes were found in glutamine and citrate. In blood, 6-phosphogluconate increased 5-fold; glucose, 1.4-fold and glucose 6-phosphate, 1.8-fold. The metabolism of glucose in the rat brain, via both the Embden-Meyerhof pathway and the hexose monophosphate shunt, was investigated by injecting [U-14C]glucose or [2-14C]glucose, and that via the hexose monophosphate shunt alone by injecting [3,4-14C]glucose. The total radioactive yield of amino acids in the rat brain was 5.63 mumol at 20 min after injection of [U-14C]glucose, or 5.82 mumol after injection of [2-14C]glucose; by contrast, it was 0.62 mumol after injection of [3,4-14C]glucose. The treatment of rats with 6-aminonicotinamide showed significant decreases in these values, owing to decreases in the radioactive yields of glutamate, glutamine, aspartate, gamma-aminobutyrate, and alanine+glycine+serine. Glutamate isolated from the brain contained approximately 43% of its radioactivity in carbon 1 after injection of [3,4-14C]glucose, in contrast to 13% and 18% after injection of [U-14C]glucose and [2-14C]glucose, respectively, in both the control and treated rats. The calculations based on these findings showed that approximately 69% of the 14C-labelled glutamate was formed from [14C]acetyl coenzyme A (acetyl CoA) and the residual 31% by 14CO2 fixation of pyruvate after injection of [3,4-14C]glucose in both control and treated rats. The results gave direct evidence that glutamate and gamma-aminobutyrate in the brain were formed by metabolism of glucose via the hexose monophosphate shunt as well as via the Embden-Meyerhof pathway. From the radioactive yields of glutamate formed via [14C]acetyl CoA it was estimated that approximately 7.8% of the total glucose utilized was channelled via the hexose monophosphate shunt. Assuming that [14C]glutamate formed by carbon-dioxide fixation of pyruvate was also dependent on the metabolism of glucose through the hexose monophosphate shunt, the estimated value was approximately 9.5% of the total glucose converted into glutamate. The results of the present investigation, taken in conjunction with other findings, suggest that the utilization of glucose via the hexose monophosphate shunt is functionally important in the rat brain.     

A 14CO2 ratios method for detecting pyruvate carboxylation

The pattern of oxidative metabolism of pyruvate may be assessed by comparing the steady-state 14CO2 production from four isotopes in identical samples. The assay requires measuring the ratios of steady-state 14CO2 production from two isotope pairs, [2-14C]pyruvate:[3-14C]pyruvate and [1-14C]acetate:[2-14C]acetate. These ratios are defined as the "pyruvate 14CO2 ratio" and the "acetate 14CO2 ratio," respectively. If pyruvate is metabolized exclusively via pyruvate dehydrogenase (PDH), the two ratios will be identical. Alternatively, if any pyruvate enters the tricarboxylic acid (TCA) cycle via pyruvate carboxylation (PC), the pyruvate 14CO2 ratio will be less than the acetate 14CO2 ratio. If pyruvate enters the TCA cycle only through PC (with oxaloacetate and fumarate in equilibrium) the pyruvate 14CO2 ratio will approach a value of 1.0. An equation is presented for the quantitative evaluation of pyruvate oxidation by these two pathways. We have used this method to detect relative changes in the pattern of pyruvate metabolism in rat liver mitochondria produced by exposure to 1 mM octanoyl carnitine, a compound known to alter the PC:PDH activity ratio. The major advantages of the method are (i) that it provides a sensitive method for detecting pyruvate carboxylation at physiological pyruvate concentrations and (ii) that it provides a method for distinguishing between effects on pyruvate transport and effects on pyruvate oxidation.     

The metabolism of fluoroacetate in lettuce

1. Whole lettuce plants were incubated with (1) [1-(14)C]acetate, (2) fluoroacetate followed by [1-(14)C]acetate, (3) fluoro[1-(14)C]acetate, (4) fluoro[2-(14)C]acetate or (5) S-carboxy[(14)C]methylglutathione. 2. Fluoroacetate did not affect the expiration of (14)CO(2) from [1-(14)C]acetate and only a small amount of (14)CO(2) was produced from either fluoro[1-(14)C]-acetate or fluoro[2-(14)C]acetate in 43h. 3. Fluoroacetate at 50mg/kg wet wt. doubled the plant citrate concentration after 43h incubation, and depending on the age and size of the plant 50-100% of the compound was metabolized. 4. With both fluoro[1-(14)C]acetate and fluoro[2-(14)C]acetate all the radioactivity except that in the CO(2) was found in the water-soluble acid fraction. About 2% was in fluorocitrate and the remainder, apart from unchanged fluoroacetate, was in a number of compounds devoid of fluorine but containing nitrogen and sulphur. These were peptide-like and could be separated by chromatography on an amino acid analyser. 5. Identical compounds were obtained from the spontaneous reaction between iodo[2-(14)C]acetate and glutathione, the major product being S-carboxymethylglutathione. 6. S-Carboxymethylcysteine was also isolated and its mass spectrum compared with a commercial sample. 7. Reaction rates of all the monohaloacetates with glutathione were studied at pH7 at 25 degrees C. No reaction was observed with fluoroacetate. 8. The metabolism of fluoroacetate by lettuce is discussed in relation to that of aliphatic and aromatic halogen compounds, including fluoroacetate, by mammalian liver and to the metabolism of fluoroacetate by different plants reported by other workers.     

Metabolism of [2-14C]acetate and its use in assessing hepatic Krebs cycle activity and gluconeogenesis

To examine the fate of the carbons of acetate and to evaluate the usefulness of labeled acetate in assessing intrahepatic metabolic processes during gluconeogenesis, [2-14C]acetate, [2-14C]ethanol, and [1-14C]ethanol were infused into normal subjects fasted 60 h and given phenyl acetate. Distributions of 14C in the carbons of blood glucose and glutamate from urinary phenylacetylglutamine were determined. With [2-14C]acetate and [2-14C]ethanol, carbon 1 of glucose had about twice as much 14C as carbon 3. Carbon 2 of glutamate had about twice as much 14C as carbon 1 and one-half to one-third as much as carbon 4. There was only a small amount in carbon 5. These distributions are incompatible with the metabolism of [2-14C]acetate being primarily in liver. Therefore, [2-14C]acetate cannot be used to study Krebs cycle metabolism in liver and in relationship to gluconeogenesis, as has been done. The distributions can be explained by: (a) fixation of 14CO2 from [2-14C]acetate in the formation of the 14C-labeled glucose and glutamate in liver and (b) the formation of 14C-labeled glutamate in a second site, proposed to be muscle. [1,3-14C]Acetone formation from the [2-14C]acetate does not contribute to the distributions, as evidenced by the absence of 14C in carbons 2-4 of glutamate after [1-14C]ethanol administration.     

Recovery of malondialdehyde in urine as a 2,4-dinitrophenylhydrazine derivative analyzed with high-performance liquid chromatography

Malondialdehyde (MDA) in urine was measured as a 2,4-dinitrophenylhydrazine (DNPH) derivative using high-performance liquid chromatography (HPLC) for the analysis. MDA standard coeluted with a peak obtained from rat urine after i.p. administration of MDA standard. This peak was also the only peak containing 14C after injection of a [14C]MDA standard, and was shown by mass spectrometry to contain 1-(2,4-dinitrophenyl)pyrazole, the derivative formed when MDA is treated with DNPH. Depending on the amount given (0.3-5.5 mumol), the recovery (after 24 h sampling period) in urine was 0.7-2.6%. This apparent non-linear kinetics may relate to several factors, such as dose-dependent metabolism. However, the peak urinary concentration approached the expected plasma concentration and reproducible recovery data were obtained, suggesting that MDA was passively excreted in a reasonably stable form. These data indicate that monitoring MDA excretion in urine can give useful information about lipid peroxidation in vivo.     

Carbon dioxide fixation and mixotrophic metabolism by strain DCB-1, a dehalogenating anaerobic bacterium

Fixation by strain DCB-1 of CO2 carbon into cell material and organic acids occurred during growth on pyruvate both with and without thiosulfate. By using sodium [14C]bicarbonate and sodium [2-14C]pyruvate, the isotopic composition of products and cells was investigated. Up to 70% of cell carbon was derived from CO2. CO2 carbon was also incorporated into succinate, formate, and acetate. Both carbons of acetate underwent exchange reactions with CO2, although the carboxyl-group exchange was twice as fast. Because strain DCB-1 uses CO2 as its major but not sole carbon source while deriving energy from pyruvate metabolism, we describe its metabolism as mixotrophic. Other mixotrophic conditions also supported growth. Lactate or butyrate, which could not support growth in mineral medium, could replace pyruvate as the oxidizable substrate only when acetate was added to the medium.     

Carbon dioxide fixation and mixotrophic metabolism by strain DCB-1, a dehalogenating anaerobic bacterium.

Fixation by strain DCB-1 of CO2 carbon into cell material and organic acids occurred during growth on pyruvate both with and without thiosulfate. By using sodium [14C]bicarbonate and sodium [2-14C]pyruvate, the isotopic composition of products and cells was investigated. Up to 70% of cell carbon was derived from CO2. CO2 carbon was also incorporated into succinate, formate, and acetate. Both carbons of acetate underwent exchange reactions with CO2, although the carboxyl-group exchange was twice as fast. Because strain DCB-1 uses CO2 as its major but not sole carbon source while deriving energy from pyruvate metabolism, we describe its metabolism as mixotrophic. Other mixotrophic conditions also supported growth. Lactate or butyrate, which could not support growth in mineral medium, could replace pyruvate as the oxidizable substrate only when acetate was added to the medium.     

Radiorespirometry evidence for the discrimination between 13C-enriched glucose and unlabelled glucose molecules by Paracoccus denitrificans

Paracoccus denitrificans was grown on either unlabelled glucose, [1-13C]glucose or [6-13C]glucose as the sole carbon source for growth. The cells were then incubated with a range of 14C-glucose substrates to compare the 14CO2-evolution rates between cells grown on the glucose and the 13C-labelled glucose. Cells grown on 13C-glucose had significantly faster rates of 14CO2-evolution than those grown on unlabelled glucose. The % yields of 14CO2, per [1-14C]-, [6-14C]- and [U-14C]glucose supplied were also substantially greater than those measured for cells grown on unlabelled glucose. The data indicated that growth of Paracoccus on 13C-enriched glucose substrates resulted in cells with notably different 14C-glucose oxidation metabolism compared to that observed in cells grown on unlabelled glucose.     

Metabolic interactions between glucose, glycerol, alanine and acetate in Leishmania braziliensis panamensis promastigotes

13C-nuclear magnetic resonance (NMR) spectroscopy was used to investigate the products of glycerol and acetate metabolism released by Leishmania braziliensis panamensis promastigotes and also to examine the interaction of each of these substrates with glucose or alanine. The NMR data were supplemented by measurements of the rates of oxygen consumption and substrate utilization, and of 14CO2 production from 14C-labeled substrate. Cells incubated with [2-13C]glycerol released acetate, succinate and D-lactate in addition to CO2. Cells incubated with acetate released only CO2. More succinate C-2/C-3 than C-1/C-4 was released from both [2-13C]glycerol and [2-13C]glucose, indicating that succinate was formed predominantly by CO2 fixation followed by reverse flux through part of the Krebs cycle. Some redistribution of the position of labeling was also seen in alanine and pyruvate, suggesting cycling through pyruvate/oxaloacetate/phosphoenolpyruvate. Cells incubated with combinations of 2 substrates consumed oxygen at the same rate as cells incubated with 1 or no substrate, even though the total substrate utilization had increased. When promastigotes were incubated with both glycerol and glucose, the rate of glucose consumption was unchanged but glycerol consumption decreased about 50%, and the rate of 14CO2 production from [1,(3)-14C]glycerol decreased about 60%. Alanine did not affect the rates of consumption of glucose or glycerol, but decreased 14CO2 production from these substrates by increasing flow of label into alanine. Although glucose decreased alanine consumption by 70%, it increased the rate of 14CO2 production from [U-14C]- and [l-14C]alanine by about 20%.(ABSTRACT TRUNCATED AT 250 WORDS)     

Synthesis of radiolabeled acetyl-coenzyme A from sodium acetate

The synthesis of high specific radioactivity [14C]-acetyl-Coenzyme A from [14C]sodium acetate, 2,6-dichlorobenzoic acid, 1,1'-carbonyldiimidazole, and CoA is reported. Starting with 1 mumol of [14C]sodium acetate, this method yields pure [14C]acetyl-CoA in yields approaching 40%. Chromatography on a reversed-phase ODS column was used to separate acetyl-CoA from Coenzyme A and side products. The acetylating agent is apparently a reaction intermediate, acetylimidazole.     

Sulfate-Dependent Interspecies H(2) Transfer between Methanosarcina barkeri and Desulfovibrio vulgaris during Coculture Metabolism of Acetate or Methanol

We compared the metabolism of methanol and acetate when Methanosarcina barkeri was grown in the presence and absence of Desulfovibrio vulgaris. The sulfate reducer was not able to utilize methanol or acetate as the electron donor for energy metabolism in pure culture, but was able to grow in coculture. Pure cultures of M. barkeri produced up to 10 mumol of H(2) per liter in the culture headspace during growth on acetate or methanol. In coculture with D. vulgaris, the gaseous H(2) concentration was 相似文献   

Metabolism of 1,25-dihydroxyvitamin D3: evidence for side-chain oxidation.

Approximately 7% of a 650-pmol dose of 25-hydroxyl[26,27-14C]vitamin D3 and 25% of a 325-pmol dose of 1,25-dihydroxyl[26,27-14C]vitamin D3 are metabolized to 14CO2 by vitamin D deficient rats. Nephrectomy prevents the metabolism of 25-hydroxy[26,27-14C]vitamin D3 to 14CO2 but not that of 1,25-dihydroxy[26,27-14C]vitamin D3. Less than 5% of the 14C from 24,25-dihydroxy[26,27-14C]vitamin D3 is metabolized to 14CO2. Feeding diets high in calcium and supplemented with vitamin D3 markedly diminishes the amount of 14CO2 formed from 25-hydroxy[26,27-14C]vitamin D3 but not that from 1,25-dihydroxyl[26,27-14C]vitamin D3. These results provide strong evidence that only 1-hydroxylated vitamin D compounds and especially 1,25-dihydroxyvitamin D3 undergo side-chain oxidation and cleavage to yield an unknown metabolite and CO2.     

Metabolism of organic compounds in anaerobic,hydrothermal sulphate-reducing marine sediments

Previous studies of hot (>80 degrees C) microbial ecosystems have primarily relied on the study of pure cultures or analysis of 16S rDNA sequences. In order to gain more information on anaerobic metabolism by natural communities in hot environments, sediments were collected from a shallow marine hydrothermal vent system in Baia di Levante, Vulcano, Italy and incubated under strict anaerobic conditions at 90 degrees C. Sulphate reduction was the predominant terminal electron-accepting process in the sediments. The addition of molybdate inhibited sulphate reduction in the sediments and resulted in a linear accumulation of acetate and hydrogen over time. [U-14C]- acetate was completely oxidized to 14CO2, and the addition of molybdate inhibited 14CO2 production by 60%. [U-14C]-glucose was oxidized to 14CO2, and this was inhibited when molybdate was added. When the pool sizes of short-chain fatty acids were artificially increased, radiolabel from [U-14C]-glucose accumulated in the acetate pool. L-[U-14C]-glutamate, [ring-14C]-benzoate and [U-14C]-palmitate were also anaerobically oxidized to 14CO2 in the sediments, but molybdate had little effect on the oxidation of these compounds. These results demonstrate that natural microbial communities living in a hot, microbial ecosystem can oxidize acetate and a range of other organic electron donors under sulphate-reducing conditions and suggest that acetate is an important extracellular intermediate in the anaerobic degradation of organic matter in hot microbial ecosystems.     

The role of carbon dioxide in the metabolism of adult Haemonchus contortus, in vitro

Adult Haemonchus contortus worms simultaneously excrete and fix CO2. Their initial content of CO2 was measured as 4.55 mumoles/100 mg wet weight and their excretion rate in air as 1 mumol/100 mg wet weight/h for at least 4 h. When the worms were incubated either aerobically or anaerobically with 14CO2 most of the metabolized radioactivity was associated with propan-1-ol and propionate but small amounts were found in succinate and lactate. No radioactivity was associated with ethanol or acetate, two major catabolites of glucose. Stepwise degradation of the metabolized radioactive propanol and propionate showed that all the radioactivity in both compounds was associated with carbon atom no. 1. These results show that H. contortus has much in common with the anaerobic energy metabolism of Ascaris lumbricoides but they are not inconsistent with the utilization of the tricarboxylic acid cycle by the worm. H. contortus worms were found to metabolize their excretory products. When they were incubated with either [2,3-14C]succinate or [2-14C]acetate, 14CO2 was excreted under aerobic but not under anaerobic conditions. These results are consistent with a pathway similar to that used by Ascaris operating aloneunder anaerobic conditions and together with the tricarboxylic acid cycle under aerobic conditions.     

Phenobarbital selectively modulates the glucagon-stimulated activity of adenylate cyclase by depressing the lipid phase separation occurring in the outer half of the bilayer of liver plasma membranes.

The pattern of incorporation of radioactivity from [1-14C]acetate and [2-14C]acetate into the polyprenyl side-chain of ubiquinones in bacteria (Azotobacter vinelandii, Pseudomonas sesami, Escherichia coli and Rhodopseudomonas capsulata) was studied. For this purpose, a new degradation method involving a modified Barbier-Wieland reaction of laevulinic acid was developed, and used along with the iodoform reaction. Both C-1 and C-2 of acetate were incorporated exclusively into C-2 of laevulinic acid suggesting that the well-known pathway through acetoacetyl-CoA ('acetoacetate pathway') was not operative in these bacteria. An alternative pathway ('acetolactate pathway'), starting with pyruvate and acetaldehyde as the distal precursors, and utilizing the reactions of leucine and valine metabolism, was postulated. It was also postulated that C-1 of acetate is incorporated not directly, but after oxidation to CO2. The pattern of incorporation of radioactivity from [U-14C]valine, [U-14C]alanine and NaH14CO3 into the side-chain of ubiquinone of R. capsulata was in agreement with the operation of the 'acetolactate pathway'.     

Ketone body utilization for energy production and lipid synthesis in isolated rat brain capillaries

Isolated brain capillaries from 2-month-old rats were incubated for 2 h in the presence of [3-14C]acetoacetate, D-3-hydroxy[3-14C]butyrate, [U-14C]glucose, [1-14C]acetate or [1-14C]butyrate. Labelled CO2 was collected as an index of oxidative metabolism and incorporation of label precursors into lipids was determined. The rate of CO2 production from glucose was slightly higher than from the other substrates. Interestingly, acetoacetate was oxidized at nearly the same rate as glucose. This shows that ketone bodies could be used as a source of energy by brain capillaries. Radiolabelled substrates were also used for the synthesis of lipids, which was suppressed by the addition of albumin. The incorporation of [U-14C]glucose in total lipids was 10-times higher than that from other precursors. However, glucose labelled almost exclusively the glycerol backbone of phospholipids, especially of phosphatidylcholine. Ketone bodies as well as glucose were incorporated mainly into phospholipids, whereas acetate and butyrate were mainly incorporated into neutral lipids. The contribution to fatty acid synthesis of various substrates was in the following order: butyrate greater than or equal to acetate greater than ketone bodies greater than or equal to glucose. All precursors except glucose were used for sterol synthesis. Glucose produced almost exclusively the glycerol backbone of phospholipids.