Kinases and phosphatases of hepatic glycogen metabolism during fasted to refed transition in normal and streptozotocin-induced diabetic rats.

Normal and streptozotocin-induced diabetic rats were fasted for 24 hours and refed for 4 hours. Changes in the activities of glycogen metabolizing enzymes in liver were followed during this period. In normal rats, hepatic glycogen content increased gradually after the onset of food intake. The percent of active glycogen synthase increased to a peak value at 1h which coincided with a significant (P less than 0.02) increase in synthase phosphatase activity. Phosphorylase alpha and the percent of alpha increased significantly (P less than 0.01) after the meal which correlated with similar increases in cAMP-dependent protein kinase and phosphorylase kinase activities. Activation of enzymes involved in both synthesis and degradation of glycogen during fasted to refed transition indicate a probable substrate cycling. In diabetic livers, there was marked decrease in the activities of glycogen metabolizing enzymes and their levels did not alter significantly in response to the meal indicating a poor turnover of glycogen.     

Amino acid metabolizing enzymes in rat submaxillary gland, normal or neoplastic, and in pancreas.

The activities of 12 enzymes, many related to ornithine metabolism, were measured in rat submaxillary gland, submaxillary gland tumors and pancreas. In submaxillary gland, the activities of arginase, ornithine aminotransferase, pyrroline-5-carboxylate reductase and glutamine synthetase were high, but no ornithine transcarbamylase or proline oxidase could be detected. In the fetal submaxillary gland, arginase was at almost adult levels while ornithine aminotransferase reached 50% of its adult value postnatally. Submaxillary tumors deviated from their cognate tissue by lower levels of amino acid metabolizing enzymes and by high concentrations of thymidine kinase. In pancreas, none of the pyrroline-5-carboxylate metabolizing enzymes were as high as in either liver or submaxillary gland. The outstanding activities were those of gamma-glutamyl transpeptidase and glutamate dehydrogenase. Although arginase activities in submaxillary gland and pancreas were quantitatively similar, they differed qualitatively: submaxillary gland contained the same variant as liver while the pancreatic isozymes resembled those of other nonhepatic tissues.     

Modulatory Effect of Taurine on 7,12‐Dimethylbenz(a)Anthracene‐Induced Alterations in Detoxification Enzyme System,Membrane Bound Enzymes,Glycoprotein Profile and Proliferative Cell Nuclear Antigen in Rat Breast Tissue

The modulatory effect of taurine on 7,12‐dimethylbenz(a)anthracene (DMBA)‐induced breast cancer in rats was studied. DMBA (25 mg/kg body weight) was administered to induce breast cancer in rats. Protein carbonyl levels, activities of membrane bound enzymes (Na⁺/K⁺ATPase, Ca²⁺ATPase, and Mg²⁺ATPase), phase I drug metabolizing enzymes (cytochrome P450, cytochrome b5, NADPH cytochrome c reductase), phase II drug metabolizing enzymes (glutathione‐S‐transferase and UDP‐glucuronyl transferase), glycoprotein levels, and proliferative cell nuclear antigen (PCNA) were studied. DMBA‐induced breast tumor bearing rats showed abnormal alterations in the levels of protein carbonyls, activities of membrane bound enzymes, drug metabolizing enzymes, glycoprotein levels, and PCNA protein expression levels. Taurine treatment (100 mg/kg body weight) appreciably counteracted all the above changes induced by DMBA. Histological examination of breast tissue further supported our biochemical findings. The results of the present study clearly demonstrated the chemotherapeutic effect of taurine in DMBA‐induced breast cancer.     

In vivo effects of vanadate on hepatic glycogen metabolizing and lipogenic enzymes in insulin-dependent and insulin-resistant diabetic animals

The insulin-mimetic action of vanadate is well established but the exact mechanism by which it exerts this effect is still not clearly understood. The role of insulin in the regulation of hepatic glycogen metabolizing and lipogenic enzymes is well known. In our study, we have, therefore, examined the effects of vanadate on these hepatic enzymes using four different models of diabetic and insulin-resistant animals. Vanadate normalized the blood glucose levels in all animal models. In streptozotocin-induced diabetic rats, the amount of liver glycogen and the activities of the active-form of glycogen synthase, both active and inactive-forms of phosphorylase, and lipogenic enzymes like glucose 6-phosphate dehydrogenase and malic enzyme were decreased and vanadate treatment normalized all of these to near normal levels. The other three animal models (db/db mouse, sucrose-fed rats and fa/fa obese Zucker rats) were characterized by hyperinsulinemia, hypertriglyceridemia, increases in activities of lipogenic enzymes, and marginal changes in glycogen metabolizing enzymes. Vanadate treatment brought all of these values towards normal levels. It should be noted that vanadate shows differential effects in the modulation of lipogenic enzymes activities in type I and type II diabetic animals. It increases the activities of lipogenic enzymes in streptozotocin-induced diabetic animals and prevents the elevation of activities of these enzymes in hyperinsulinemic animals. The insulin-stimulated phosphorylation of insulin receptor subunit and its tyrosine kinase activity was increased in streptozotocin-induced diabetic rats after treatment with vanadate. Our results support the view that insulin receptor is one of the sites involved in the insulin-mimetic actions of vanadate.     

Differential effects of chronic endosulfan exposure to male rats in relation to hepatic drug metabolism and androgen biotransformation

Chronic endosulfan exposure in rats led to considerable increase in the activities of drug metabolizing enzymes, whereas it had inhibitory effect on the activities of enzymes involved in the androgen biotransformation. Endosulfan also produced a dose- and duration-dependent increase in microsomal lipid peroxidation. The alterations produced after shorter duration showed much variation with respect to the dose levels and exposure period of endosulfan studied. The above biochemical changes were reversed after endosulfan withdrawal.     

Enzymes of starch metabolism in Nicotiana tabacum callus

Activities of enzymes of starch metabolism were determined in tobacco callus grown in light or darkness and in the presence or absence of gibberellic acid. There was a higher rate of starch turnover in light-grown cultures, as judged by the activities of synthetic and degradative enzymes. Gibberellic acid-treated tissues contained a lower level of starch than the corresponding control tissue. This decrease could be correlated with the activity of phosphorylase. Cultured tissue and seedling material were found to have comparable levels of activity for the starch metabolizing enzymes.     

Effect of Sargassum polycystum (Phaeophyceae)-sulphated polysaccharide extract against acetaminophen-induced hyperlipidemia during toxic hepatitis in experimental rats

The effect of Sargassum polycystum crude extract on lipid metabolism was examined against acetaminophen-induced (800 mg/kg body wt., intraperitoneally) hyperlipidemia during toxic hepatitis in experimental rats. The animals intoxicated with acetaminophen showed significant elevation in the levels of cholesterol, triglycerides and free fatty acid in both serum and liver tissue. The levels of tissue total lipids and serum LDL-cholesterol were also elevated with depleted levels of serum HDL-cholesterol and tissue phospholipid. The acetaminophen-induced animals showed significant alterations in the activities of lipid metabolizing enzymes serum lecithin cholesterol acyl transferase (LCAT) and hepatic triglyceride lipase (HTGL). The levels of liver tissue fatty acids (saturated, mono and polyunsaturated) such as palmitic acid, stearic acid, oleic acid, linoleic acid, arachidonic acid and linolenic acid monitored by gas chromatography were considerably altered in acetaminophen intoxicated animals when compared with control animals. The prior oral administration of Sargassum polycystum (200 mg/kg body wt./day for a period of 15 days) crude extract showed considerable prevention in the severe disturbances of lipid profile and metabolizing enzymes triggered by acetaminophen during hepatic injury. Liver histology also showed convincing supportive evidence regarding their protective nature against fatty changes induced during acetaminophen intoxication. Thus the present study indicates that the protective nature of Sargassum polycystum extract may be due to the presence of active compounds possessing antilipemic property against acetaminophen challenge. (Mol Cell Biochem 276: 89–96, 2005)     

The respirative breakdown of glucose by Saccharomyces cerevisiae: an assessment of a physiological state

Cells of Saccharomyces cerevisiae exhibiting respirative glucose metabolism in continuous culture were able to use ethanol as a co-substrate. The ethanol uptake rate was dependent on the residual respirative capacity of the cells. The activities of gluconeogenic enzymes and of malate dehydrogenase were higher in cells degrading glucose respiratively than in cells metabolizing glucose respiro-fermentatively, but were lower than in cells growing on ethanol only. The pattern of distribution of the mitochondrial cytochromes was similar but the differences were less distinct. In synchronously growing cells, the activities of gluconeogenic enzymes and of malate dehydrogenase oscillated, with activities increasing during the budding phase. The increase was preceded by the appearance of ethanol in the culture medium.     

‘台农1号’芒果果实发育过程中的糖分积累与相关酶活性研究

以‘台农1号’芒果为材料,测定了果实生长发育过程中淀粉、蔗糖、葡萄糖和果糖含量以及淀粉酶、蔗糖代谢相关酶———酸性转化酶(AI)、中性转化酶(NI)、蔗糖合成酶(SS)和蔗糖磷酸合成酶(SPS)的活性,并对果实中糖组分与酶活性的关系进行了分析.结果显示,(1)台农1号芒果果实属于单S型生长曲线,发育前期主要积累淀粉、葡萄糖和果糖,果实成熟软化时,淀粉酶活性降至最低,淀粉水解,蔗糖快速积累.(2)酸性转化酶活性在果实整个发育过程中维持最高,完熟时略有降低;蔗糖磷酸合成酶在果实发育前期略有降低,完熟时升至最高;蔗糖合成酶和中性转化酶活性在整个发育期一直很低且较稳定.(3)淀粉含量与淀粉酶活性呈显著正相关,与SPS活性呈极显著负相关,蔗糖、葡萄糖含量均与SPS、SS呈显著、极显著的正相关;果糖含量与SS呈极显著的正相关.研究表明,芒果成熟时淀粉分解、酸性转化酶活性的降低,且蔗糖合成酶和蔗糖磷酸合成酶活性的增加是引起果实蔗糖积累的主要因子.     

The effects of soman in vitro on catechol-O-methyltransferase and monoamine oxidase activities in rabbit tissues

Soman (pinacolyl methylphosphonofluoridate) not only increases acetylcholine levels by inhibiting cholinesterases, it also alters the levels of some other neurotransmitters including norepinephrine, dopamine, and serotonin. Soman also causes an alteration in the activities of the enzymes metabolizing norepinephrine when it is administered to animals. Because these alterations may result from indirect effects on the enzymes, the effects of in vitro application of soman on catechol-O-methyltransferase (COMT) and monoamine oxidase (MAO) activities in rabbit tissues were investigated. Enzyme activities were determined in rabbit lung, liver, cerebellum, cerebrum, brain stem, mesenteric artery, pulmonary artery, renal artery, central ear artery, thoracic aorta, and diaphragm. MAO and COMT activities were not affected by soman in any tissues tested, except the lung and liver, where the activity of COMT was increased (p less than 0.05). Thus, reported effects of soman in vivo on norepinephrine, dopamine, or serotonin concentrations, and MAO and COMT activities do not seem to result from direct effects on the activities of these amine-metabolizing enzymes.     

Effect of cadmium on pulmonary and renal microsomal drug metabolizing enzymes of the guinea-pig

1. The effect of acute cadmium (Cd) treatment on pulmonary and renal microsomal aniline 4-hydroxylase and ethylmorphine N-demethylase enzyme activities of adult male guinea-pigs were assessed 72 hr following a single dose of Cd ion (2 mg Cd2+/kg i.p.). Tissue and microsomal Cd levels were also determined. 2. There were no significant differences between either lung or kidney tissue weights, microsomal protein contents or enzyme activities of Cd treated and control animals. 3. The tissues and microsomes of Cd-treated animals were found to have significantly higher levels of Cd than those of control animals. In Cd treated animals, tissue and microsomal Cd levels of kidney were found to be higher than that of lung. 4. In vitro addition of cadmium chloride (CdCl2) to incubation mixtures produced concentration related inhibitions of microsomal drug metabolizing enzymes in each tissue. However, in vitro effect of CdCl2 was found to be stronger on drug metabolizing enzymes of kidney than those of lung. In addition, while the strength of Cd effect was more pronounced on the activity of ethylmorphine N-demethylase than that of aniline 4-hydroxylase in the lung, the opposite was observed in the kidney.     

Effect of sodium molybdate on carbohydrate metabolizing enzymes in alloxan-induced diabetic rats

We evaluated the effect of sodium molybdate on carbohydrate metabolizing enzymes and mitochondrial enzymes in diabetic rats. Diabetic rats showed a significant reduction in the activities of glucose metabolising enzymes like hexokinase, glucose-6-phosphate dehydrogenase, glycogen synthase and in the level of glycogen. An elevation in the activities of aldolase, glucose-6-phosphatase, fructose 1,6- bisphosphatase, glycogen phosphorylase and in the level of blood glucose were also observed in diabetic rats when compared to control rats. The activities of mitochondrial enzymes isocitrate dehydrogenase, alpha-ketoglutarate dehydrogenase, succinate dehydrogenase, malate dehydrogenase, NADH-dehydrogenase and cytochrome-C-oxidase were also significantly lowered in diabetic rats. Molybdate administration to diabetic rats reversed the above changes in a significant manner. From our observations, we conclude that administration of sodium molybdate regulated the blood sugar levels in alloxan-induced diabetic rats. Sodium molybdate therapy not only maintained the blood glucose homeostasis but also altered the activities of carbohydrate metabolising enzymes. Molybdate therapy also considerably improved the activities of mitochondrial enzymes, thereby suggesting its role in mitochondrial energy production.     

Nitrogen Metabolizing Enzyme Activities In the Free-Living Soil Amoebae Acanthamoeba Castellanii, Acanthamoeba Polyphaga and Hartmannella Vermiformis

ABSTRACT. Free-living soil amoebae consume a wide variety of food, including algae, yeast, small protozoa and especially bacteria, which they digest to fulfil their nutritional requirements. Amoebae play an active role in the nitrogen mineralization in soils due to their nitrogen metabolizing capacities. However, little is known about nitrogen metabolizing enzyme activities in these free-living soil amoebae. In this study a number of key enzymes involved in the nitrogen metabolism of the axeaically cultivated free-living soil amoebae Acanthamoeba castellanii, Acanthamoeba polyphaga and two different strains of Hartmannella vermiformis were determined. the specific enzyme activities for exponential growth phase ceils were calculated and it appeared that the species tested possessed urate oxidase, glutamine synthetase, NADH-dependent glutamate dehydrogenase, glutamate oxaloacetate transaminase and glutamate pyruvate transaminase activity. Glutamate synthase activity could not be detected in any of these species. the levels of specific activities varied depending on the enzymes tested. For all species the highest activities were detected for the transaminase reactions yielding glutamate, and for glutamate dehydrogenase. A general conclusion is that the pathway of nitrogen assimilation in free-living soil amoebae is similar to the one observed for other eukaryotes. Differences in specific activities were detected between the species.     

Diurnal Changes in Maize Leaf Photosynthesis : III. Leaf Elongation Rate in Relation to Carbohydrates and Activities of Sucrose Metabolizing Enzymes in Elongating Leaf Tissue

Maize (Zea mays L. cv. Pioneer 3184) leaf elongation rate was measured diurnally and was related to diurnal changes in the activities of sucrose metabolizing enzymes and carbohydrate content in the elongating portion of the leaf. The rate of leaf elongation was greatest at midday (1300 hours) and was coincident with the maximum assimilate export rate from the distal portion of the leaf. Leaf elongation during the light period accounted for 70% of the total observed increase in leaf length per 24 hour period. Pronounced diurnal fluctuations were observed in the activities of acid and neutral invertase and sucrose phosphate synthase. Maximum activities of sucrose phosphate synthase and acid invertase were observed at 0900 hours, after which activity declined rapidly. The activity of sucrose phosphate synthase was substantially lower than that observed in maize leaf source tissue. Neutral invertase activity was greatest at midday (1200 hours) and was correlated positively with diurnal changes in leaf elongation rate. There was no significant change in the activity of sucrose synthase over the light/dark cycle. Sucrose accumulation rate increased during a period when leaf elongation rate was maximal and beginning to decline. Maximum sucrose concentration was observed at 1500 hours, when the activities of sucrose metabolizing enzymes were low. At no time was there a significant accumulation of hexose sugars. The rate of starch accumulation increased after the maximum sucrose concentration was observed, continuing until the end of the light period. There was no delay in the onset of starch mobilization at the beginning of the dark period, and essentially all of the starch was depleted by the end of the night. Mobilization of starch in the elongating tissue at night could account for a significant proportion of the calculated increase in the tissue dry weight due to growth. Collectively, the results suggested that leaf growth may be controlled by the activities of certain sucrose metabolizing enzymes and may be coordinated with assimilate export from the distal, source portion of the leaf. Results are discussed with reference to diurnal photoassimilation and export in the distal, source portion of the leaf.     

Glycogen metabolizing enzymes in brain

Three enzymes, glycogen phosphorylase, glycogen synthase, and phosphoglucomutase were evaluated in subcellular fractions and in brain regions. Also the development of each of these enzymes was evaluated in whole brain homogenates. Each enzyme increased during the first three weeks of post partum in a manner that is similar to the development of glycolytic enzymes during this period. The specific activity of each enzyme in various subcellular fractions indicated that the enzymes were primarily soluble. Also unlike the glycolytic enzyme phosphoglycerate kinase, the glycogen metabolizing enzymes had a lower specific activity in synaptosomes than in particle free supernatant fractions of homogenates. Regarding regional distribution small (less than twofold) but significant differences were seen between different brain areas. An inverse relationship between the glycogen metabolizing enzymes and hexokinase was observed, that is, regions highest in glycogen synthase and glycogen phosphorylase were lowest in hexokinase and regions highest in hexokinase were lowest in the glycogen metabolizing enzymes.     

Transmural distribution of glucose metabolizing enzymes across the left and the right ventricle heart walls in three different mammalian species

The transmural distribution of five glucose metabolizing enzymes (hexokinase; glucose-6-phosphate dehydrogenase; phosphofructokinase; aldolase; and lactate dehydrogenase) were explored in the left and in the right ventricle wall of rat, ox and pig hearts. The levels of most of these enzyme activities were different in the different animal species and (within the same species) in the two ventricles. Most of these enzyme activities were found to be non-uniformly distributed across the left (but not across the right) ventricle wall. Differences in the transmural distribution of enzyme activities were detected among the three examined mammalian species.     

The gap junctional intercellular communication is no prerequisite for the stabilization of xenobiotic metabolizing enzyme activities in primary rat liver parenchymal cells in vitro

Summary In primary monocultures of adult rat liver parenchymal cells (PC), the activities of the xenobiotic metabolizing enzymes microsomal epoxide hydrolase (mEH_b), soluble epoxide hydrolase (sEH), glutathione S-transferases (GST), and phenolsulfotransferase (ST) were reduced after 7 d to values below 33% of the initial activities. Furthermore, the gap junctional intercellular communication (GJIC), measured after microinjection by dye transfer, decreased from 90% on Day 1 to undetectable values after 5 d in monoculture. Co-culture of PC with nonparenchymal rat liver epithelial cells (NEC) increased (98% on Day 1) and stabilized (82% on Day 7) the homotypic GJIC of PC. Additionally, most of the measured xenobiotic metabolizing enzyme activities were well stabilized over 1 wk in co-culture. Because GJIC is one of several mechanisms playing an important role in cell differentiation, the importance of GJIC for the stabilization of xenobiotic metabolizing enzymes in PC was investigated. PC in monoculture were, therefore, treated with 2% dimethyl sulfoxide (DMSO), a differentiation promoting factor, and 1,1,1-trichloro-2,2,-bis (p-chlorophenyl) ethane (DDT) (10 μg/ml), a liver tumor promotor and inhibitor of GJIC, was given to co-cultures of PC with NEC. DMSO significantly stabilized (68% on Day 7), while DDT significantly inhibited (8% on Day 7) homotypic GJIC of PC in the respective culture systems. In contrast, the activities of mEH_b, sEH, GST, and ST were not affected in the presence of DMSO or DDT. These results lead to the assumption that the differentiation parameters measured in this study (i.e., homotypic GJIC and the activities of xenobiotic metabolizing enzymes) are independently regulated in adult rat liver PC.     

Multi-biomarker responses in the freshwater mussel Dreissena polymorpha exposed to polychlorobiphenyls and metals

Contaminant related changes in behavioral, phase I and II metabolizing enzymes and pro-oxidant/antioxidant processes in the freshwater mussels Dreissena polymorpha exposed to metals and PCBs were assessed. Behavioral and biochemical responses including filtering rates, key phase I, II and antioxidant enzymes and levels of metallothioneins, glutathione, lipid peroxidation and DNA strand breaks were determined in digestive glands of mussels after being exposed to sublethal levels of mercury chloride, methyl mercury, cadmium and Aroclor 1260 during 5 days. In 7 out of 12 responses analyzed, mussels showed significant differences across treatments. Unusual properties of measured ethoxyresorufin-O-deethylase (EROD) activities indicated that mussels lack an inducible CYP1A enzymatic activity. Despite of using similar exposure levels, inorganic and organic mercury showed different biomarker patterns of response with methyl mercury being more bio-available and unable to induce metallothionein proteins. Mussels exposed to Cd presented higher levels of metallothioneins and an enhanced metabolism of glutathione, whereas those exposed to Aroclor showed their antioxidant glutathione peroxidase related enzyme activities inhibited. Although there was evidence for increased lipid peroxidation under exposure to inorganic and organic mercury, only mussels exposed to Aroclor had significant greater levels than those in controls.     

Parameters of energy and nitrogen metabolism in rats under insulin-induced hypoglycemia

Repeated severe insulin-induced hypoglycemia in rats has led to an increase in aminotransferase, glutaminase, and glutamate dehydrogenase activities in the liver; protease activities in tissues; and in blood serum levels of free fatty acids, urea, and uric acid. These changes are indicative of gluconeogenesis activation in animals exposed to hyperinsulinization. Decreased rates of glycolysis and glycogenolysis, reduced activities of NADP-dependent dehydrogenases, and substantial changes in the activities of enzymes responsible for metabolism of nucleotides and transmitter amino acids have been observed in the brain. All these changes are mainly associated with hypoglycemia and activation of the contrainsular system and can play a significant role in pathogenesis of posthypoglycemic encephalopathy.