Effects of high dietary methionine on activities of selected enzymes in the liver of kittens (felis domesticus)

• 1.1. Growing male kittens were fed an 18% casein diet supplemented with 2, 3, or 4% l-methionine (MET) for 6 weeks.
• 2.2. Free MET concentration in liver increased 30-fold and cystathionine two- to three-fold; the activity of adenosyl-MET transferase and cystathionase also increased but remained lower than previously found in rats.
• 3.3. Taurine concentration in liver decreased in cats fed excess MET and appeared to depend on taurine intake.
• 4.4. Alanine aminotransferase activity was high in all groups while serine dehydratase activity was very low.
• 5.5. Pyruvate kinase and malic enzyme activities which are normally low in cat liver increased after excess MET. Also, glucose 6-phosphate and 6-phosphogluconate dehydrogenases increased.
• 6.6. Cat liver metabolism showed limited adaptation to an excess dietary intake of methionine compared to that found in rats.

     

Enzymes of fructose metabolism in the intestinal mucosa of the rat (Rattus norvegicus). Localization along the small intestine; consequences of dietary fructose

• 1.1. The activities of all the eight enzymes of conversion of fructose to glucose, of all the three key enzymes of glycolysis and of the two dehydrogenases of pentose shunt were determined in proximal and distal mucosa of small intestine.
• 2.2. With the exception of hexokinase, all of these enzymes have an activity significantly higher in the proximal than distal mucosa.
• 3.3. The gradient along the intestine is particularly important for the three enzymes which are typical for fructose metabolism (ketohexokinase, triokinase and fructose-1-phosphate aldolase), for glucose-6-phosphatase and for phosphofructokinase.
• 4.4. The effects of fructose diet on the enzyme activities are compatible with the results, described in other papers, concerning the final products of metabolism.
• 5.5. The increase of fructose metabolism appears to result mainly from the stimulation of the activities of ketohexokinase and fructose-1-phosphate aldolase which control all the pathways of ketohexose utilization.
• 6.6. The activation of glucose-6-phosphatase, in comparison with the other enzymes which are involved in glucose-6-phosphate metabolism, explains the appearance of the ability to synthesize glucose with fructose as substrate. This enzyme is the only key enzyme of fructose to glucose conversion which responds to fructose feeding in distal mucosa.
• 7.7. The activities of hexokinase and phosphofructokinase are not increased by fructose feeding.
• 8.8. The activity of pyruvate kinase. the only key glycolytic enzyme which is necessarily implicated when fructose is the substrate, is stimulated but less than the typical enzymes of fructose metabolism.
• 9.9. But, because of its quantitative importance, the glycolytic pathway is responsible for the most part of the observed increase of fructose utilization.
• 10.10. The responses of pyruvate kinase, glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase activities to fructose feeding are similar in the two parts of small intestine.
• 11.11. The activities of ketohexokinase, triokinase and glucose-6-phosphate isomerase are stimulated only in the proximal small intestine mucosa.
• 12.12. The other enzyme activities which are stimulated in proximal segment are also increased in distal segment.
• 13.13. All segments of small bowel show adaptive changes to dietary manipulation but not necessarily for all their functions.
• 14.14. The gradient of enzyme activities from the proximal to the distal small intestine persists despite dietary modification, but the data do not determine that this gradient is intrinsic or that it is not intrinsic.

     

Effect of diet and essential amino acids gavage on young rat amino acid metabolism enzymes

• 1.1. The effects of a high-fat, high-energy diet and essential plus semi-essential amino acid gavage on pup rats have been studied (60–65 animals).
• 2.2. The activities of alanine transaminase, adenylate deaminase, glutamine synthetase and serine dehydratase have been tested in liver and muscle.
• 3.3. Plasma was used for the estimation of proteins, urea, amino acids, glucose, lactate, 3-hydroxy-butyrate and acetoacetate.
• 4.4. Liver and muscle glutamine synthetase activities are increased by diet and gavage administered. Hepatic serine dehydratase is inhibited by a cafeteria diet but activated by amino acid gavage. Adenylate deaminase is inhibited by diet and gavage in the liver, but gavage does not affect this enzyme activity in muscle. Liver alanine transaminase is increased by the diet; in the muscle, cafeteria diet and amino acid gavage showed the highest values for this enzyme.
• 5.5. In the plasma, the increase in lactate produced by the diet is inhibited by the amino acids provided. Cafeteria-fed pups showed lower urea levels and higher 3-hydroxybutyrate concentrations in the plasma.
• 6.6. Intracellular glucose is diminished by cafeteria diet. In contrast, the blood cell amino acid concentration increases with diet and gavage supplied.

     

NAD(P)H dehydrogenase from rabbit and rat liver: Purification and some properties

• 1.1. NAD(P)H dehydrogenase from rabbit liver was purified to electrophoretic homogeneity using a procedure also found applicable for the rat liver enzyme.
• 2.2. Rabbit and rat liver enzymes showed different behaviour in isoelectric focusing and different K_m values and turnover numbers.
• 3.3. Both enzymes were inhibited to similar extents by warfarin.
• 4.4. The rabbit enzyme is composed of two subunits of mol. wt 27,000 and contained 1 FAD group per subunit.
• 5.5. Some absorption and circular dichroism properties of the rat enzyme are shown.

     

The effects of duodenal glucose infusion on some hepatic enzyme activities in sheep

• 1.1. Two experiments were performed to examine the effects of duodenal glucose infusion on hepatic enzyme activities in sheep.
• 2.2. Glucose infusion significantly increased the specific activities of phosphofructokinase, pyruvate kinase and 6-phosphogluconate dehydrogenase and significantly reduced the specific activity of glucose-6-phosphatase suggesting that the pathways of glucose breakdown are increased, and gluconeogenesis decreased, in glucose-infused animals.
• 3.3. These results are discussed in relation to the effects of diet on liver metabolism in sheep.

     

Lipid peroxidation affects catalytic properties of rat liver mitochondrial monoamine oxidases and their sensitivity to proteolysis

• 1.1. Lipid peroxidation (LPO) in rat liver mitochondria decreased the activity of monoamine oxidase (MAO) with physiological substrates serotonin and 2-phenylethylamine (by 15–30%) and induced deamination of glucosamine, which was highly sensitive to selective MAO A inhibitor pirlindole.
• 2.2. The LPO-induced changes in catalytic properties of MAOs are accompanied by their increased susceptibility to trypsinolysis, however sensitivity to inhibition by imipramine, chlorpromazine and spermine are insignificantly changed.
• 3.3. It is suggested that these results reflect LPO-induced conformational changes of enzyme molecules in membrane rather than their membrane topography.

     

Glycolytic enzymes of fowl and turkey spermatozoa

• 1.1. It was confirmed that, under anaerobic conditions, fowl spermatozoa formed lactate from glucose thirteen times faster than turkey spermatozoa.
• 2.2. The profiles of glycolytic enzyme activities were similar for spermatozoa from both species; however fowl spermatozoal activities were generally 2- to 4-fold higher.
• 3.3. Exceptions were glycerophosphate mutase and lactate dehydrogenase activities which were respectively 9.5 and 41 times greater in fowl spermatozoa.
• 4.4. In both species, spermatozoal glyceraldehyde-3-phosphate dehydrogenase had the lowest activity of the glycolytic enzymes.

     

The effect of hypoxia on carbohydrate metabolism in flounder (Platichthys flesus L.)—II. High energy phosphate compounds and the role of glycolytic and gluconeogenetic enzymes

• 1.1. ATP, ADP, AMP, energy charge potential and total adenylates in heart, kidney and muscle are relatively unaffected by environmental hypoxia. In the liver, hypoxia causes a 90% drop in ATP, a rise in ADP and AMP, and a drop in energy charge potential and total adenylates. In the muscle tissue ATP concentration is stabilized by a large creatine phosphate pool.
• 2.2. Hexokinase activity in the heart is 20 times higher than in the swimming muscle, and thus the heart has a high potential for utilizing exogenous glucose as an anaerobic substrate.
• 3.3. The role of creatine phosphate in regulating muscle glycolysis is discussed on background of the strong inhibition of muscle phosphofructokinase by physiological concentrations of creatine phosphate.
• 4.4. Flounder heart has a dominating M-type lactate dehydrogenase which is identical to the muscle enzyme by electrophoretic and kinetic criteria. This improves the anaerobic capabilities of the flounder heart compared to other fish hearts.
• 5.5. Both liver and kidney have high activities of the gluconeogenetic enzymes glucose-6-phosphatase, fructose-1,6-diphosphatase, and phosphoenolpyruvate carboxykinase and both are capable of synthesizing glucose from [¹⁴C]lactate. Because of more favorable energy conditions in the kidney this organ may substitute the liver as a gluconeogenetic organ during hypoxia.

     

Effects of the nonsteroidal anti-inflammatory drug piroxicam on energy metabolism in the perfused rat liver

• 1.1. The actions of piroxicam, a nonsteroidal and noncarboxylic anti-inflammatory drug, on the metabolism of the isolated perfused rat liver were investigated. The main purpose was to verify if piroxicam is also active on glycogenolysis and energy metabolism, as demonstrated for several carboxylic nonsteroidal anti-inflammatories.
• 2.2. Piroxicam increased oxygen consumption in livers from both fed and fasted rats.
• 3.3. Piroxicam increased glucose release and glycolysis from endogenous glycogen (glycogenolysis).
• 4.4. Gluconeogenesis from lactate plus pyruvate was inhibited.
• 5.5. The action of piroxicam on oxygen consumption was blocked by antimycin A, but not by atractyloside.
• 6.6. The action of piroxicam in the perfused rat liver metabolism seems to be a consequence of its action on mitochondria.
• 7.7. It can be concluded that inhibition of energy metabolism and stimulation of glycogenolysis are not specific properties of carboxylic nonsteroidal anti-inflammatory drugs.

     

Prenatal induction of tyrosine aminotransferase in rat liver

• 1.1. Hepatic tyrosine aminotransferase activity from adult rat can be resolved into four components on hydroxylapatite column.
• 2.2. A similar profile of enzyme distribution can be obtained from late foetal liver.
• 3.3. Insulin administration to pregnant rats result in induction of two isoenzymes of tyrosine aminotransferase in foetal rat liver. Similarly Cyclic AMP injection to foetal rats in utero results in the induction of the same two forms of the enzyme.
• 4.4. Triaminolone injection to foetal rats in utero leads to the induction of three of the isoenzymes of tyrosine aminotransferase.

     

The effect of hypoxia on carbohydrate metabolism in flounder (Platichthys flesus L.)—I. Utilization of glycogen and accumulation of glycolytic end products in various tissues

• 1.1. Resting oxygen consumption at 10°C did not change from normoxia (150 mm Hg) down to an oxygen tension of 55 mm Hg for the flounder, Platichtys flesus.
• 2.2. Flounders exposed to hypoxia showed increased levels of blood glucose and lactate, dependent on the degree of hypoxia.
• 3.3. Due to hypoxia glycogen was depleted in the liver and swimming muscle but in the heart there was no significant change.
• 4.4. Liver glucose increased after 7 hr of hypoxia. Heart and muscle glucose did not change but the absolute glucose concentration in the heart was five times higher than in the muscle.
• 5.5. There is a transient accumulation of lactate in heart, liver and kidney after 7 hr of hypoxia while lactate accumulation in the swimming muscle is significant only after 21 hr of hypoxia.
• 6.6. Succinate only accumulated in the liver while alanine accumulated in muscle, heart and liver.

     

Interaction of lipogenic substrates in porcine adipose tissue in vitro

• 1.1. Porcine adipose tissue was incubated with radiolabeled glucose, acetate or lactate. Saturation curves indicated that lactate > glucose > acetate in providing two-carbon units for fatty-acid synthesis.
• 2.2. Competition between individual substrates indicated that lactate was the best lipogenic substrate.
• 3.3. Incubation of all three substrates at concentrations observable in serum indicated that at 5.56mM, glucose was the preferred lipogenic substrate in the presence of 0.1 mM acetate and 1.0 mM lactate.
• 4.4. At elevated concentrations (18.52mM glucose, 1.0 mM acetate and 10.0 mM lactate), acetate and lactate were preferred to glucose as lipogenic substrates.

     

Stearyl-CoA desaturation capacity of the rat liver during regeneration after partial hepatectomy

• 1.1. Stearyl-CoA desaturase activity was measured in microsomes isolated from regenerating rat liver over a period of 11 days.
• 2.2. The stearyl-CoA desaturation capacity of the liver recovered by the fourth day after partial hepatectomy.
• 3.3. Return to normal enzyme activity coincided with the normalization of the ratio between stearic and oleic acids in microsomes.

     

Purification and characterization of carbonyl reductases from bovine liver cytosol and microsome. the cytosolic enzyme has a novel 3α/17β-hydroxysteroid dehydrogenase activity

• 1.1. Carbonyl reductase, which is distributed in both cytosolic and microsomal fractions in bovine liver, were purified to homogeneity on 12.5% sodium dodecylsulfate-polyacrylamide gel electrophoresis and shown to have molecular weights of 32 kDa and 68 kDa, respectively.
• 2.2. Both carbonyl reductases can catalyze the reduction of many carbonyl compounds including ketone, quinones and aldehyde with relatively low K_m values.
• 3.3. From the absorption spectrum result, microsomal carbonyl reductase closely resembles cytochrome P-450 reductase.
• 4.4. Cytosolic carbonyl reductase is a novel enzyme which can act on both testosterone and androsterone at low concentration.

     

The regulation of glucose 6-phosphate dehydrogenase from Dicentrarchus labrax (bass) liver

• 1.1. Kinetic constant values of the reaction catalyzed by bass liver glucose 6-phosphate dehydrogenase show to be modified between 10 and 40°C.
• 2.2. The Arrhenius plot between 10 and 50°C shows two slopes with different activation energies.
• 3.3. These results suggest a regulation of this enzyme by environmental temperature.
• 4.4. Kinetics of ATP inhibition were examined between pH 6.2 and 7.8: patterns and K_i values obtained are affected by the pH variation.
• 5.5. NADH is an effective inhibitor of bass glucose 6-phosphate dehydrogenase but this enzyme does not show NAD-linked activity.
• 6.6. Kinetics of pyridoxal 5′-phosphate inhibition have indicated the presence of a lysine in the catalytic site for NADP⁺.

     

Effect of methyl methacrylate on mitochondrial function and structure

• 1.1. Treatment of isolated rat liver mitochondria with methyl methacrylate (MM) produced membrane disruption as evidenced by the release of citrate synthase, and changes in the ultrastructure of mitochondria.
• 2.2. At concentration 0.1%, MM uncoupled oxidative phosphorylation as evidenced by stimulation of state 4 respiration supported either by pyruvate plus malate or succinate (+rotenone) and ATP-ase activity in intact mitochondria.
• 3.3. At concentration 1% MM stimulated ATP-ase activity in intact mitochondria and succinate (+rotenone) oxidation at state 4 and was without effect on this substrate oxidation at state 3.
• 4.4. MM inhibited pyruvate plus malate oxidation either at state 3 or in the presence of uncoupling agents.
• 5.5. MM inhibited the NADH oxidase of electron transport particles at a concentration which failed to inhibit either succinic oxidase or the NADH-ferricyanide reductase activity.
• 6.6. The data presented suggest that in the isolated mitochondria MM inhibits NADH oxidation in the vicinity of the rotenone sensitive site of complex I.
• 7.7. The general conclusion is that MM may block an electron transport and to uncouple oxidative phosphorylation in rat liver mitochondria. The overall in vitro effect would be to prevent ATP synthesis which could result in cell death under in vivo conditions.

     

Kinetic properties of cat liver microsomal glucose-6-phosphatase

• 1.1. Cat liver microsomes contain the multifunctional enzyme glucose-6-phosphatase.
• 2.2. High specificity was shown for the phosphohydrolase as well as for the transferase activity.
• 3.3. Both activities have high V_max values determined in optimized conditions.
• 4.4. The phosphate transfer with carbamyl-phosphate as a phosphoryl donor and d-glucose as acceptor is consistent with a random mechanism in which the binding of one substrate decreases the enzyme's affinity for the second substrate.

     

The phospholipase activities present in preheparin mouse plasma are inhibited by antiserum to hepatic lipase

• 1.1. Preheparin plasma from mice, but not rats or man, contains high levels of phospholipase A and lysophospholipase activities which are distinct from lecithin:cholesterol acyltransferase (LCAT).
• 2.2. Neither the phospholipase A nor the lysophospholipase activities in preheparin plasma are inhibited by incubation in the presence of protamine sulphate or high salt concentrations.
• 3.3. When mouse plasma is incubated in the presence of an antiserum specific for rat hepatic triacylglycerol lipase (HTGL), the phospholipase activities are abolished.
• 4.4. These observations suggest that the phospholipase activities are attributable to the action of HTGL, which, in the mouse appears to be a freely circulating enzyme, whereas for other species this enzyme only appears in the blood following administration of heparin.

     

Partial purification of rat liver cytoplasmic acetyl-CoA synthetase; Characterization of some properties

• 1.1. Rat liver cytoplasmic acetyl-CoA synthetase was partially purified (purification factor = 23, yield = 30%).
• 2.2. The apparent K_ms for acetate, coenzyme A, ATP and MgCl₂ were determined and found to be 52.5 μM, 50.5 μM, 570 μM and 1.5 mM, respectively.
• 3.3. The partially-purified enzyme showed a low affinity for short-chain carbon substrates other than acetate.
• 4.4. The properties of the partially-purified enzyme were compared with those of enzymes from other sources.