Citric Acid Cycle Activity Research Articles

Effect of ethanol on ketone metabolism.

Ketonuria has been observed in alcoholics. To study the mechanism of this effect, healthy, volunteers were given adequate diets (36% of calories as lipid and 15% as protein) for 18 days, with isocaloric replacement of carbohydrate (46% of calories) by either ethanol or additional fat. The latter resulted in a high fat diet, with 82% of calories as lipid. After about 1 wk of alcohol, massive and persistent ketonuria developed. Compared with the control period, there was a 30-fold increase in fasting blood acetoacetate and beta-hydroxybutyrate (P < 0.001). With the high fat diet, acetoacetate and beta-hydroxybutyrate increased 8- to 10-fold (P < 0.001). In the postprandial state, ethanol also induced hyperketonemia, but less markedly than when ethanol followed an overnight fast. With low fat diets (5% of calories), alcohol (46% of total calories) did not induce ketonuria or hyperketonemia, suggesting that a combination of alcohol and dietary fat is necessary. The addition of alcohol to rat liver slices did not affect ketogenesis. In rats pretreated with alcohol for 3 days, however, ketonemia developed, hepatic glycogen was decreased, and liver slices (incubated with palmitate-(14)C and glucose) had a significant increase in acetoacetate production, when compared to carbohydrate pretreated controls. Alcohol pretreatment or addition of alcohol in vitro had no effect on acetoacetate utilization by rat diaphragms, and decreased only slightly the conversion of beta-hydroxybutyrate-(14)C to (14)CO(2). Thus, the hyperketonemia and ketonuria observed after alcohol consumption cannot be attributed to an immediate effect of alcohol, but is the consequence of a delayed change in intermediary metabolism characterized by increased hepatic ketone production from fatty acids, possibly linked to ethanol-induced glycogen depletion and depression of citric acid cycle activity.

On the coupling of respiration to cation transport in slices of rat liver

1. 1. Rat-liver slices utilizing endogenous substrate respired at a rate of 9.2 μl O 2 per mg fat-free dry wt. per h, in a medium containing 5 mM K + and 161 mM Na +. Inhibition of the active transport of Na + and K + by ouabain, reduced the rate of respiration of these slices by 2.4 μl O 2 per mg per h (26% inhibition). 2. 2. In a medium containing 75 mM K + and 91 mM Na +, the control rate of respiration was 10.1 μl O 2 per mg fat-free dry wt. per h; ouabain lowered this by only 0.8 μl per mg per h (8% inhibition). It is suggested that the latter portion of the total O 2 uptake is coupled to the energy requirements of ion transport (‘transport-coupled respiration’). The additional inhibition caused by ouabain in the 5 mM K + medium appears to be due to changes in the oxidative metabolism resulting from the altered cation composition of the intracellular environment (‘cation-sensitive respiration’). 3. 3. Malonate and ethanol, at concentrations which are known to inhibit citric acid cycle activity, have little effect on ion transport. 4. 4. In the presence of ethanol or malonate, inhibition of ion transport (by ouabain, or K +-free medium) inhibits respiration only by an amount similar to the transport-coupled respiration (0.65–1.16 μl per mg per h). The cation-sensitive portion of the respiration appears to be due to the provision of reducing equivalents by the citric acid cycle. 5. 5. Approximate calculations are made of the amount of energy made available by the transport-coupled respiration, and this is compared to an estimate of the minimal energy requirement of the Na + transport.

Lack of platelet response to stimulation in the Wiskott-Aldrich syndrome.

Two striking abnormalities were found in the platelets from three boys with the Wiskott-Aldrich syndrome and their mother: lack of aggregation with epinephrine, and lack of metabolic response to stimulation with polystyrene-latex particles and with epinephrine. Whereas normal platelets reacted with an increase of eight to 12 times in citric acid cycle activity to the addition of polystyrene-latex particles, and with an increase of two to three times to epinephrine stimulation, these metabolic reactions were practically absent in the platelets from the affected children and severely depressed also in the platelets of the mother.

Age dependent changes of certain peptide hydrolases and dehydrogenases in bovine dental pulp.

The concentrations of certain peptide hydrolases and enzymes of the aerobic and anaerobic catabolic cycles in the fibroblasts of bovine dental pulp have been examined as a function of the developmental stage of the tissue. It was shown that the enzyme content does not change uniformly during the aging process. Anaerobic catabolic pathways remained unchanged or increased with cell maturity whereas the citric acid cycle activity decreased. Peptide hydrolases remained essentially constant.

Fatty acid oxidation, citric acid cycle activity, and morphology of mitochondria in diabetic rat liver.

SummaryPalmitate and oleate oxidation in isolated mitochondria from alloxan diabetic rat liver were shown to be elevated two or threefold over normal. These increases were accompanied by enlargement of mitochondria as observed by electron microscopy. These metabolic and structural changes were reversed by treating the diabetic rat with insulin. The activities of citric acid cycle enzymes in MT were unchanged in the diabetic state. It is suggested that insulin regulates LCFA oxidation in the liver by an effect on MT structure and function.

Oxidative metabolism of bovine spermatozoa.

Suspensions of washed bovine sperm (phosphate buffer, pH 7.4) were incubated at 37 °C for 1 h with pyruvate-3-14C and in some cases, with oxaloacetate. Oxygen consumption and 14CO2 evolution were measured. Radioactive citrate, malate, fumarate, α-ketoglutarate, and oxaloacetate were found following incubation. The latter two compounds were positively identified by melting-point and specific-activity determinations of their 2,4-dinitrophenylhydrazone derivatives. The results indicate citric acid cycle activity in bull sperm. Oxygen consumption and the evolution of 14CO2 from pyruvate-3-14C tended to decline when oxaloacetate was added to the sperm suspensions.

Membrane systems of mitochondria: VI. Membranes of liver mitochondria

Beef and rat liver mitochondria were isolated by procedures designed to eliminate contaminating microsomal activities (e.g., glucose 6-phosphatase and the rotenone-insensitive DPNH-cytochrome c reductase). Mitochondria thus prepared were completely competent in respect to electron transport and citric acid cycle activity. The matrix space of these mitochondria was ruled out as the site of the citric cycle activities on the basis of two lines of evidence: the inability of carboxydextran to penetrate the inner boundary membrane during the time of the release of the S fraction; and the apparent morphological integrity of the inner boundary membrane of mitochondria exposed to the action of oleate or phospholipase during the period of release of the S fraction. Liver mitochondria were fractionated into the soluble S fraction, the membranous K fraction, and the R 2 fraction. Each of these fractions accounted for about 33% of the total mitochondrial protein. The S fraction, which contained all the readily solubilizable citric cycle activities, was shown to be localized between the two boundary membranes. The enzymes of this fraction serve as spacer units which link together the two boundary membranes. The K fraction, which contained the activities of particulate complexes such as the α-ketoglutarate dehydrogenase complex, was identified with the outer membranes. Finally, the R 2 fraction, which contained all the activities of the electron transfer chain and ATPase and monoamine oxidase activity, was identified with the cristae. The repeating units of the outer membrane are devoid of projecting elements, and show up in electron micrographs as spheres, about 100 Å in diameter. Cardiolipin accounts for about 15% of the total phospholipid phosphorus of the outer membrane fraction. The cholesterol content of the outer membrane is relatively low. The analytical data for the lipid composition of the outer membrane are compatible with the thesis that the cristae and outer membranes have the same set of phospholipids and the same ratio of phospholipid to cholesterol.

Regulation by illumination of the citric acid cycle activity in Rhodopseudomonas spheroides.

Journal Article Regulation by Illumination of the Citric Acid Cycle Activity in Rhodopseudomonas spheroides Get access SHOZO TUBOI, SHOZO TUBOI Department of Biochemistry, Tohoku University School of MedicineSendai Search for other works by this author on: Oxford Academic PubMed Google Scholar GORO KIKUCHI GORO KIKUCHI Department of Biochemistry, Tohoku University School of MedicineSendai Search for other works by this author on: Oxford Academic PubMed Google Scholar The Journal of Biochemistry, Volume 59, Issue 5, May 1966, Pages 456–462, https://doi.org/10.1093/oxfordjournals.jbchem.a128327 Published: 01 May 1966 Article history Received: 09 November 1965 Published: 01 May 1966

CO2 Fixation in Opuntia Roots

Nonautotrophic CO(2) metabolism in Opuntia echinocarpa roots was studied with techniques of manometry and radiometry. The roots were grown in a one-quarter strength nutrient solution for several days; the distal 2 cm was used for physiological studies. The roots assimilated significant quantities of (14)CO(2) and appeared to show a crassulacean-type acid metabolism with respect to quality and quantity. Most of the (14)C activity was associated with the distal portion of the elongating root indicating correlation with metabolic activity. The (14)CO(2) assimilation was comparable to a crassulacean leaf succulent, but 3 times greater than that found for stem tissue of the same Opuntia species.The rates of O(2) and CO(2) exchange and estimated CO(2) fixation were 180, 123, and 57 mul/g per hour. A respiratory quotient of 0.66 was found.The products of (14)CO(2) fixation were similar in most respects to reported experiments with leaf succulents. Equilibration of the predominant malic acid with isocitric, succinic, and fumaric acids was not evident. The latter observation was interpreted as metabolic isolation of the fixation products rather than poor citric acid cycle activity.A rapid turnover of the fixed (14)CO(2) was measured by following decarboxlyation kinetics and by product analysis after a postincubation period. The first order rate constant for the steady state release was 4.4 x 10(-3) min(-1) with a half-time of 157.5 minutes. Amino acids decayed at a more rapid rate than organic acids.

Glucose metabolism in leucocytes from patients with diabetes mellitus, with and without hypercholesteremia.

The metabolism of glucose by the Embden-Meyerhof, pentose cycle and citric acid cycle pathways was determined in human polymorphonuclear leucocytes from control subjects and from patients with diabetes mellitus, with and without hypercholesteremia. In controls over 85 per cent of glucose uptake was metabolized to lactic acid by the Embden-Meyerhof pathway; about 5 per cent of glucose uptake was recovered as Co2, mostly from oxidation in the pentose cycle. Minimal citric acid cycle activity, a finding which correlated well with the paucity of mitochondria in the leucocyte, was shown by the slight and similar degree of oxidation of pyruvate and acetate. Glucose metabolism in leucocytes from diabetics differed in two respects. The per cent of glucose uptake oxidized in the pentose cycle was increased in leucocytes from all diabetics. In the insulin-treated diabetics glucose uptake and lactic acid formation were similar to controls. In contrast, glucose uptake and lactic acid formation were reduced in leucocytes from adult, latent, hypercholesteremic diabetics. Pyruvate and acetate oxidation was similar in diabetics and controls. Thus, in terms of leucocyte metabolism, hypercholesteremia in the human diabetic was correlated with reduced glycolysis and not with reduced pentose cycle activity.

Effect of Whole-body X-irradition on Glucose Oxidation by Rat Small Intestine Mucosa in Vitro

A method was developed for determining the rate of glucose oxidation by rat small intestine mucosa in vitro. Results from studies of the oxidation of carbon-14 labeled compounds indicate that the increase in glucose oxidation by rat small intestine mucosa following x irradiation is due entirely to increased citric acid cycle activity. In addition, the results suggest that x irradiation causes a decrease in oxidation of glucose by extraglycolytic pathways but does not affect the oxidation of glucose by way of the Embden-Meyerhof pathway. (C.H.)

Enzyme studies of various stages of the blowfly Phormia regina (meig.)

Investigations on carbohydrate dissimilation in the blowfly Phormia regina have been conducted. Extensive citric acid cycle activity was found to be localized in adult mitochondria, but could not be demonstrated in larvae. Cytochrome oxidase activity was greater in the adult than in larvae. Glycolysis and the pentose cycle system were present in soluble fractions from both the adult and larvae, and the pentose cycle was also indicated in the egg. The presence of three TPN-specific enzymes was demonstrated: isocitric, G-6-P, and 6-PGA dehydrogenases.