Activities of some enzymes concerned with citrate and glucose metabolism in transplanted rat hepatomas.
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ABSTRACT:
SUBMITTER: McLean P
PROVIDER: S-EPMC1264931 | biostudies-other | 1966 Mar
REPOSITORIES: biostudies-other
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Project description:1. Extractable hexokinase activity was measured in the red and white skeletal muscles of the rabbit and in the hearts and diaphragms of four animal species differing markedly in size. Activities vary over a 40-fold range, being least in white skeletal muscle of the laboratory rabbit and greatest in mouse heart. 2. Hexokinase activities correlate approximately with capacities to undertake reactions of the tricarboxylic acid cycle as determined by succinate oxidase assays. Both enzyme activities seem best related to the average contractile-energy expenditure per unit weight of muscle over an extended period, rather than to the rapidity of individual contractions. 3. Hexokinase and succinate oxidase activities cannot be related to a muscle's content of soluble pigment. They display an inverse relationship with activities of phosphorylase and glycolytic enzymes, but only within the group of rabbit skeletal muscles whose oxidative capacities are at the lower end of the observed range. 4. Total glycogen-UDP glucosyltransferase activities do not vary significantly between rabbit skeletal muscles, although those of hexokinase differ by about sixfold. On the average, glucose 6-phosphate is probably oxidized directly. However, observations cited in the literature suggest that muscles with an active hexokinase may well preferentially accumulate glycogen when glucose is present in excess of the fibres' capacity to oxidize it. 5. When considered with published results obtained in vivo, the present findings indicate that phosphorylase has a minor role in the energy expenditure of muscles with a predominantly oxidative metabolism. In these, the major substrates appear to be blood glucose, fatty acids and possibly lipids. 6. The histochemical criteria by which muscle fibres are commonly described as red or white are inadequate.
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Project description:The activity of 3-phosphoglycerate dehydrogenase was high in tissues of high cell-renewal capacity, and was increased in neonatal and regenerating liver and, more markedly, in hepatomas. Serine hydroxymethyltransferase activity was present in hepatomas, whereas other enzymes of serine utilization (serine dehydratase and serine aminotransferase) were absent. This enzymic imbalance couples serine biosynthesis preferentially to nucleotide precursor formation in cancer cells.
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Project description:1. The activities of enzymes of the urea cycle [carbamoyl phosphate synthetase, ornithine transcarbamoylase, argininosuccinate synthetase, argininosuccinase (these last two comprising the arginine-synthetase system) and arginase] have been measured in control, alloxan-diabetic and glucagon-treated rats. In addition, measurements were made on alloxan-diabetic rats treated with protamine-zinc-insulin. 2. Treatment of rats with glucagon for 3 days results in a marked increase in the activities of three enzymes of the urea cycle (carbamoyl phosphate synthetase, argininosuccinate synthetase and argininosuccinase). The pattern of change in the alloxan-diabetic group is very similar to that of the glucagon-treated group, although the magnitude of the change was much greater. 3. Comparison was made of the actual and potential rate of urea synthesis in normal and diabetic rats. In both groups the potential rate of urea production, as measured by the activity of the rate-limiting enzyme, argininosuccinate synthetase, slightly exceeds the actual rate of synthesis by liver slices in the presence of substrates. The relative activities of the actual and potential rates were similar in the two groups of animals, this ratio being 1:0.70. 4. In the alloxan-diabetic rats treated with protamine-zinc-insulin for 2.5 or 4 days there was a marked increase in liver weight. This was associated with a rise in the total hepatic activity of the urea-cycle enzymes located in the soluble fraction of the cell (the arginine-synthetase system and arginase) after 2.5 days of treatment. After 4 days of treatment the concentration of these enzymes/g. of liver decreased, and the total hepatic content then reverted to the untreated alloxan-diabetic value. 5. No effects of glucagon or of insulin in vitro could be found on the rate of urea production by liver slices. 6. The present results are discussed in relation to how far this pattern of change is typical of conditions resulting in a high urea output, and comparison has been made with other values in the literature.
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Project description:The activities of two mitochondrial enzymes concerned in the utilization of acetoacetate, namely 3-oxoacid CoA-transferase and acetoacetyl-CoA thiolase, were high throughout the suckling and weanling period in brown adipose tissue of the rat. In contrast, 3-hydroxybutyrate dehydrogenase activity was comparatively low during this period. The activity of cytosolic acetoacetyl-CoA synthetase (involved in lipogenesis) declined after birth and remained low until the pups were weaned. Experiments with brown-adipose-tissue slices from weanling rats indicated that 70% of the [3-14C]acetoacetate utilized was oxidized to 14CO2, and this value was not altered appreciably by the addition of glucose and insulin.
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Project description:1. Changes in the content and concentration of glycogen and in the activity of a number of enzymes involved in glucose and glycogen metabolism were studied in the rat hemidiaphragm after unilateral denervation. 2. After nerve section the tissue hypertrophies; this hypertrophy is said to be confined to the smaller red fibres and not to the white. 3. The total hexokinase activity increases, whereas that of total glycogen phosphorylase decreases. The specific activity of phosphorylase a, determined after Halothane anaesthesia, remains fairly constant. 4. In fed animals the denervated tissue stores less glycogen, but in the early stages its glycogen content does not fall on starvation. 5. The effect of denervation on the specific activities of several other characteristically white-fibre enzymes are not consistent with the response of glycogen phosphorylase; the increase in content of glyceraldehyde 3-phosphate dehydrogenase and lactate dehydrogenase is thought to be related to proliferation of the sarcoplasmic reticulum. 6. The ratio of lactate dehydrogenase M/H subunits increases at the height of the hypertrophy, but then declines as the mass of the tissue falls. 7. The chronology of these changes in enzyme activities suggests a multiplicity of distinct responses after nerve section not consistent with any one model, either specific fibre development or reversion to de-differentiated, foetal-type metabolism.
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Project description:The activities of glycerol 3-phosphate dehydrogenase (EC 1.1.1.8), glycerol kinase (EC 2.7.1.30), lactate dehydrogenase (EC 1.1.1.27), "malic' enzyme (L-malate-NADP+ oxidoreductase; EC 1.1.1.40) and the beta-oxoacyl-(acyl-carrier protein) reductase component of the fatty acid synthetase complex were measured in nine hepatoma lines (8 in rats, 1 in mouse) and in the livers of host animals. With the single exception of Morris hepatoma 16, which had unusually high glycerol 3-phosphate dehydrogenase activity, the activities of glycerol 3-phosphate dehydrogenase and glycerol kinase were highly correlated in normal livers and hepatomas (r = 0.97; P less than 0.01). The activities of these two enzymes were not strongly correlated with the activities of any of the other three enzymes. The primary function of hepatic glycerol 3-phosphate dehydrogenase appears to be in gluconeogenesis from glycerol.
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Project description:With a yearly production of about 39 million tons, brewer's spent grain (BSG) is the most abundant brewing industry byproduct. Because it is rich in fiber and protein, it is commonly used as cattle feed but could also be used within the human diet. Additionally, it contains many bioactive substances such as hydroxycinnamic acids that are known to be antioxidants and potent inhibitors of enzymes of glucose metabolism. Therefore, our study aim was to prepare different extracts-A1-A7 (solid-liquid extraction with 60% acetone); HE1-HE6 (alkaline hydrolysis followed by ethyl acetate extraction) and HA1-HA3 (60% acetone extraction of alkaline residue)-from various BSGs which were characterized for their total phenolic (TPC) and total flavonoid (TFC) contents, before conducting in vitro studies on their effects on the glucose metabolism enzymes α-amylase, α-glucosidase, dipeptidyl peptidase IV (DPP IV), and glycogen phosphorylase α (GPα). Depending on the extraction procedures, TPCs ranged from 20-350 µg gallic acid equivalents/mg extract and TFCs were as high as 94 µg catechin equivalents/mg extract. Strong inhibition of glucose metabolism enzymes was also observed: the IC50 values for α-glucosidase inhibition ranged from 67.4 ± 8.1 µg/mL to 268.1 ± 29.4 µg/mL, for DPP IV inhibition they ranged from 290.6 ± 97.4 to 778.4 ± 95.5 µg/mL and for GPα enzyme inhibition from 12.6 ± 1.1 to 261 ± 6 µg/mL. However, the extracts did not strongly inhibit α-amylase. In general, the A extracts from solid-liquid extraction with 60% acetone showed stronger inhibitory potential towards a-glucosidase and GPα than other extracts whereby no correlation with TPC or TFC were observed. Additionally, DPP IV was mainly inhibited by HE extracts but the effect was not of biological relevance. Our results show that BSG is a potent source of α-glucosidase and GPα inhibitors, but further research is needed to identify these bioactive compounds within BSG extracts focusing on extracts from solid-liquid extraction with 60% acetone.
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Project description:The posttranslational modification (PTM) in protein occurs in a regiospecific manner. In addition, the most commonly occurring PTMs involve similar residues in proteins such as acetylation, ubiquitylation, methylation and sumoylation at the lysine residue and phosphorylation and O-GlcNAc modification at serine/threonine residues. Thus, the possibility of modification sites where two such PTMs may occur in a mutually exclusive manner (ME-PTM) is much higher than known. A recent surge in the identification and the mapping of the commonly occurring PTMs in proteins has revealed that this is indeed the case. However, in what way such ME-PTM sites are regulated and what could be their relevance in the coordinated network of protein function remains to be known. To gain such potential insights in a biological context, we analyzed two most prevalent PTMs on the lysine residue by acetylation and ubiquitylation along with the most abundant PTM in proteins by phosphorylation among enzymes involved in glucose metabolism, a fundamental process in biology. The analysis of the PTM data sets has revealed two important clues that may be intrinsically associated with their regulation and function. First, the most commonly occurring PTMs by phosphorylation, acetylation and ubiquitylation are widespread and clustered in most of the enzymes involved in glucose metabolism; and the prevalence of phosphorylation sites correlates with the number of acetylation and ubiquitylation sites including the ME-modification sites. Second, the prevalence of ME-acetylation/ubiquitylation sites is exceptionally high among enzymes involved in glucose metabolism and have distinct pattern among the subset of enzymes of glucose metabolism such as glycolysis, tricarboxylic acid (TCA) cycle, glycogen synthesis, and the irreversible steps of gluconeogenesis. We hypothesize that phosphorylation including tyrosine phosphorylation plays an important role in the regulation of ME-acetylation/ubiquitylation sites and their similar pattern among the subset of functionally related proteins allows their coordinated regulation in the normal physiology. Similarly their coordinated dysregulation may underlie the disease processes such as reprogrammed metabolism in cancer, obesity, type 2 diabetes, and cardiovascular diseases. Our hypothesis provides an opportunity to understand the regulation of ME-PTMs in proteins and their relevance at the network level and is open for experimental validation.
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Project description:Aerobic methanotrophic bacteria utilize methane as a growth substrate but are unable to grow on any sugars. In this study we have shown that two obligate methanotrophs, Methylotuvimicrobium alcaliphilum 20Z and Methylobacter luteus IMV-B-3098, possess functional glucose dehydrogenase (GDH) and gluconate kinase (GntK). The recombinant GDHs from both methanotrophs were homotetrameric and strongly specific for glucose preferring NAD+ over NADP+. GDH from Mtm. alcaliphilum was most active at pH 10 (Vmax = 95 U/mg protein) and demonstrated very high Km for glucose (91.8 ± 3.8 mM). GDH from Mb. luteus was most active at pH 8.5 (Vmax = 43 U/mg protein) and had lower Km for glucose (16 ± 0.6 mM). The cells of two Mtm. alcaliphilum double mutants with deletions either of the genes encoding GDH and glucokinase (gdh─/glk─) or of the genes encoding gluconate kinase and glucokinase (gntk─/glk─) had the lower glycogen level and the higher contents of intracellular glucose and trehalose compared to the wild type strain. The gntk─/glk─ knockout mutant additionally accumulated gluconic acid. These data, along with bioinformatics analysis, demonstrate that glycogen derived free glucose can enter the Entner-Doudoroff pathway or the pentose phosphate cycle in methanotrophs, bypassing glycolysis via the gluconate shunt.
| S-EPMC8062543 | biostudies-literature
Project description:1. The activities of the enzymes of the urea cycle were measured in rat liver after feeding with a diet containing ethionine for 2 weeks. This treatment resulted in a decrease in the activity of ornithine transcarbamoylase, which fell to half the control value, while arginase increased by about 40%. The remaining enzymes of the urea cycle were unchanged at this time of treatment. These results are discussed in relation to the known effects of ethionine on nucleic acid synthesis. 2. The activities of glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase were measured in rat liver after feeding with a diet containing ethionine for 2 or 5 weeks. At the shorter time-period glucose 6-phosphate-dehydrogenase activity was more than doubled but 6-phosphogluconate-dehydrogenase activity remained unchanged. 3. The results are compared with similar measurements made after feeding with diets containing 4-dimethylamino-3'-methylazobenzene for 2 weeks. Striking similarities were found in the pattern of change in the enzyme activities of each of the pathways in the two treatments.
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