Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.6.1.1 (aspartate aminotransferase)
21,665 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In patients with severe alcoholic liver disease (i.e., cirrhosis), a deficiency of S-adenosylmethionine (SAMe) develops as a result of decreased SAMe synthetase activity. Whether a sizeable SAMe depletion occurs already at earlier stages of alcoholic liver disease has been the subject of debate. To address this issue, rats were fed alcohol (or isocaloric carbohydrate) in Lieber-DeCarli liquid diets containing adequate amounts of protein, vitamins, and lipotropic factors, including methionine. Alcohol feeding resulted in hepatic steatosis (without fibrosis) and unchanged SAMe synthetase activity, yet SAMe concentration was already greatly decreased. This most likely resulted from oxidative stress associated with the metabolism of alcohol and the induction of cytochrome P4502E1 (CYP2E1), which generates free radicals. Indeed, the decrease in hepatic SAMe correlated with parameters of oxidative stress, such as increased 4-hydroxynonenal (measured by gas chromatography-mass spectrometry) and diminished glutathione (GSH). Decreased GSH, occurring as a result of excessive GSH consumption caused by the oxidative stress, probably generated by enhanced utilization of SAMe, a precursor of GSH, thereby explaining the depletion of SAMe. In view of the known differences between rodents and primates in the metabolism of lipotropes, my colleagues and I have also studied the interaction between alcohol and SAMe in baboons and found again that, at early stages preceding the development of cirrhosis, there was already a significant lowering of hepatic SAMe concentration, associated with a striking oxidative stress documented by decreased levels and accelerated turnover of GSH. This was associated with increased lipid peroxidation and damage to cellular membranes, including those of the mitochondria, assessed by electron microscopy. Oral administration of SAMe resulted in its hepatic repletion with a corresponding attenuation of the ethanol-induced oxidative stress and liver injury, with significantly less GSH depletion, less increases in plasma aspartate aminotransferase (AST) levels, less leakage of mitochondrial glutamic dehydrogenase into the plasma, and fewer megamitochondria. In conclusion, (1) both in rodents and in non-human primates, significant SAMe depletion occurs already at early stages of alcoholic liver disease, despite the consumption of adequate diets; (2) the decreased hepatic SAMe concentration and the associated liver lesions, including mitochondrial injury, can be corrected with SAMe supplementation; and (3) accordingly, therapeutic administration of SAMe should be the subject of a comprehensive clinical trial to assess its capacity to attenuate early stages of alcoholic liver injury in human beings.
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PMID:S-Adenosyl-L-methionine and alcoholic liver disease in animal models: implications for early intervention in human beings. 1216 46

Many patients with rheumatoid arthritis (RA) have low plasma pyridoxal-phosphate (PLP) but a normal erythrocyte aspartate aminotransferase activity coefficient (alpha EAST), a measure of vitamin B-6 status in the erythrocytes, compared with healthy subjects. The goal of the present study was to examine the correlations of PLP levels in these two compartments (plasma and erythrocytes) with other established indices of vitamin B-6 status, and to determine which indicator better reflects functional status of vitamin B-6 in patients with RA. Multiple indices of vitamin B-6 status were measured in 33 patients with RA. Plasma PLP, urinary 4-pyridoxic acid (4-PA), net increase in plasma total homocysteine after a methionine load (DeltatHcy) and net increase in urinary xanthurenic acid after a tryptophan load (DeltaXA) were log-transformed to reach normality for statistical analyses. We found that log-plasma PLP levels were inversely correlated with both log-DeltatHcy (r = -0.368, P = 0.035) and log-DeltaXA (r = -0.333, P = 0.05). Plasma PLP was not correlated with alpha EAST or urinary 4-PA excretion. In contrast, erythrocyte PLP was inversely correlated with alpha EAST (r = -0.431, P = 0.012) and positively correlated with log-4-PA (r = 0.475, P = 0.005), but erythrocyte PLP was not correlated with the outcomes of a methionine or tryptophan load test. Erythrocyte PLP and log-4-PA, but not plasma PLP, were correlated with dietary intake of vitamin B-6 after adjusting for protein intake (r = 0.420, P = 0.015 and r = 0.333, P = 0.05, respectively). We suggest that in patients with RA, plasma PLP levels are a better diagnostic indicator of functional vitamin B-6 status than erythrocyte PLP levels.
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PMID:Plasma pyridoxal 5'-phosphate concentration is correlated with functional vitamin B-6 indices in patients with rheumatoid arthritis and marginal vitamin B-6 status. 1267 18

Alcoholic steatohepatitis (ASH) and nonalcoholic steatohepatitis (NASH) are common liver diseases in the United States. ASH and NASH occur more frequently in women than in men, and liver injury is also more severe in women. The role of estrogens in ASH has been well established, but their role in NASH has received relatively little study. The purpose of this study was to evaluate the effect of estrogens in methionine-choline deficient diet (MCDD)-induced steatohepatitis in mice. The degree of steatohepatitis was evaluated in males and in intact and ovariectomized females that were fed MCDD for 4 weeks, and in females that were fed MCDD containing tamoxifen. Hematoxylin and eosin-stained sections of livers showed marked steatohepatitis in all experimental groups. Compared to the control group, markers of hepatocyte injury such as aspartate transaminase (AST), alanine transaminase (ALT), and liver triglyceride levels increased significantly in males and in intact and ovariectomized female mice that were fed MCDD. Also, it was interesting that levels of AST and ALT increased much more in the MCDD + tamoxifen group than in the MCDD group. In female mice fed MCDD, hepatocyte proliferative and apoptotic indices increased slightly compared to mice that were fed a normal diet. Based on these results, it can be concluded that MCDD-induced steatohepatitis is comparable in male and female mice, and that ovariectomy or antiestrogen treatment had no protective effect in MCDD-induced steatohepatitis.
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PMID:Sex differences in choline-deficient diet-induced steatohepatitis in mice. 1473 94

A subfamily I aminotransferase gene homologue containing an open reading frame encoding 381 amino acid residues (Mr=42,271) has been identified in the process of the genome project of an extremely thermophilic bacterium, Thermus thermophilus HB8. Alignment of the predicted amino acid sequence using FASTA shows that this protein is a member of aminotransferase subfamily Igamma. The protein shows around 40% identity with both T. thermophilus aspartate aminotransferase [EC 2.6.1.1] and mammalian glutamine:phenylpyruvate aminotransferase [EC 2.6.1.64]. The recombinant protein expressed in Escherichia coli is a homodimer with a subunit molecular weight of 42,000, has one pyridoxal 5'-phosphate per subunit, and is highly active toward glutamine, methionine, aromatic amino acids, and corresponding keto acids, but has no preference for alanine and dicarboxylic amino acids. These substrate specificities are similar to those described for mammalian glutamine: phenylpyruvate aminotransferase. This is the first enzyme reported so far that has the glutamine aminotransferase activity in non-eukaryotic cells. As the presence of aromatic amino acid:2-oxoglutarate aminotransferase [EC 2.6.1.57] has not been reported in T. thermophilus, this enzyme is expected to catalyze the last transamination step of phenylalanine and tyrosine biosynthesis. It may also be involved in the methionine regeneration pathway associated with polyamine biosynthesis. The enzyme shows a strikingly high pKa value (9.3) of the coenzyme Schiff base in comparison with other subfamily I aminotransferases. The origin of this unique pKa value and the substrate specificity is discussed based on the previous crystallographic data of T. thermophilus and E. coli aspartate aminotransferases.
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PMID:Glutamine:phenylpyruvate aminotransferase from an extremely thermophilic bacterium, Thermus thermophilus HB8. 1476 73

Alcoholic liver disease is associated with abnormal hepatic methionine metabolism, including increased levels of homocysteine and S-adenosylhomocysteine (SAH) and reduced levels of S-adenosylmethionine (SAM) and glutathione (GSH). The concept that abnormal methionine metabolism is involved in the pathogenesis of alcoholic liver disease was strengthened by our previous findings in a micropig model where combining dietary folate deficiency with chronic ethanol feeding produced maximal changes in these metabolites together with early onset of microscopic steatohepatitis and an eightfold increase in plasma aspartate aminotransferase. The goal of the present study was to determine potential mechanisms for abnormal levels of these methionine metabolites by analyzing the transcripts and activities of transmethylation enzymes in the livers of the same micropigs. Ethanol feeding or folate deficiency, separately or in combination, decreased transcript levels of methylenetetrahydrofolate reductase (MTHFR), methionine adenosyltransferase (MAT1A), glycine-N-methyltransferase (GNMT) and S-adenosylhomocysteine hydrolase (SAHH). Ethanol feeding alone reduced the activities of methionine synthase (MS) and MATIII and increased the activity of GNMT. Each diet, separately or in combination, decreased the activities of MTHFR and SAHH. In conclusion, the observed abnormal levels of methionine metabolites in this animal model of accelerated alcoholic liver injury can be ascribed to specific effects of ethanol with or without folate deficiency on the expressions and activities of hepatic enzymes that regulate transmethylation reactions. These novel effects on transmethylation reactions may be implicated in the pathogenesis of alcoholic liver disease.
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PMID:Hepatic transmethylation reactions in micropigs with alcoholic liver disease. 1512 59

The ybdL gene of Escherichia coli codes for a protein of unknown function. Sequence analysis showed moderate homology to several vitamin B(6) dependent enzymes, suggesting that it may bind pyridoxal-5'-phosphate. The structure analysis of YbdL to 2.35 A resolution by protein crystallography verifies that it is a PLP dependent enzyme of fold type I, the typical aspartate aminotransferase fold. The active site contains a bound pyridoxal-5'-phosphate, covalently attached to the conserved active site lysine residue Lys236. The pattern of conserved amino acids in the putative substrate binding pocket of the enzyme reveals that it is most closely related to a hyperthermophilic aromatic residue aminotransferase from the archeon Pyrococcus horikoshii. Activity tests with 10 amino acids as amino-donors reveal, however, a preference for Met, followed by His and Phe, results which can be rationalized by modelization studies.
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PMID:Crystal structure and reactivity of YbdL from Escherichia coli identify a methionine aminotransferase function. 1528 32

Pathogenesis of steatohepatitis, a common liver disease, remains controversial. It is proposed that fatty liver with a second hit capable of inducing necroinflammation results in nonalcoholic steatohepatitis. Long chain and very long chain fatty acids are considered important in induction of steatohepatitis. Peroxisome proliferator-activated receptor alpha (PPARalpha) plays an important role in beta-oxidation of long chain and very long chain fatty acids and mitogenic effect caused by peroxisome proliferators in the liver. To determine the role of PPARalpha in the pathogenesis of steatohepatitis and compensatory liver cell hyperplasia, we have used PPARalpha null mice and methionine and choline deficient nutritional model. Male and female PPARalpha null mice and wild type mice were fed methionine and choline deficient diet (MCDD) or normal chow for 4 weeks. Livers were analyzed morphologically for steatosis, steatohepatitis and hepatocyte proliferation (PCNA labeling) and biochemically for triglyceride levels. In addition, serum alanine transaminase, aspartate transaminase and triglyceride levels were measured. In MCDD fed PPARalpha null mice there was severe steatohepatitis and very high liver triglyceride levels compared to wild type mice. Serum aspartate transaminase levels were also significantly higher in MCDD fed PPARalpha null mice compared to wild type mice. The severity of steatohepatitis in MCDD fed male and female PPARalpha null mice was greater compared to wild type mice fed the same diet. The PCNA labeling index was similar in PPARalpha null mice and wild type mice fed MCDD, and significantly higher in both the groups compared to the mice fed control diet. These findings indicate that defective fatty acid oxidation aggravates steatohepatitis caused by methionine and choline deficiency and further establishes the role of long chain and very long chain fatty acids in the pathogenesis of steatohepatitis. In addition, the results of this study also indicate that there is no difference between males and females in the severity of steatohepatitis induced by MCDD and lack of PPARalpha does not affect compensatory hyperplasia in the liver.
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PMID:Lack of peroxisome proliferator-activated receptor alpha in mice enhances methionine and choline deficient diet-induced steatohepatitis. 1551 75

Metabolic pathways are controlled primarily by protein degradation rates. Degradation rates, in turn, are controlled by changes in physiologic condition or nutrient supply. Vitamin B(6) is associated with a greater variety of reactions than most other vitamins. Moreover, the vitamin B(6) needs of the elderly tend to be higher than those of young adults. Neutrophils seem to be appropriate cells for assessing protein turnover as affected by macronutrients and micronutrients. Thus, we assumed that vitamin B(6) supplementation, particularly in an elderly population, would change the turnover rates of the neutrophil proteins. Protein synthesis was measured after 30 minutes of (35)S-Met incorporation followed by a 30-minute washout incubation; degradation was measured after an additional 5-hour incubation. Following protein separation, radioactive images of short-lived proteins were electronically separated into bands. Vitamin B(6) supplementation significantly increased the synthesis of most neutrophil protein bands. There was a significant decrease of 25 to 66% in the degradation rates of 235 protein bands. We even detected by statistical evaluation a 20% decrease in the degradation rates of distinct protein bands. Activation coefficients of erythrocyte aspartate aminotransferase (AC-AST) decreased markedly. There was a significant positive correlation between the decrease in AC-AST and protein degradation. The N-end rule proposes that pyridoxal 5'-phosphate decreases degradation rates of short-lived proteins by binding to lysyl residues. A biochemical model of the mechanism of cellular protein turnover, as affected by nutritional intervention, in human neutrophils is demonstrated.
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PMID:Effect of vitamin B6 supplementation on degradation rates of short-lived proteins in human neutrophils. 1553 25

Patients with rheumatoid arthritis have subnormal vitamin B6 status, both quantitatively and functionally. Abnormal vitamin B6 status in rheumatoid arthritis has been associated with spontaneous tumor necrosis factor (TNF)-alpha production and markers of inflammation, including C-reactive protein and erythrocyte sedimentation rate. Impaired vitamin B6 status could be a result of inflammation, and these patients may have higher demand for vitamin B6. The aim of this study was to determine if daily supplementation with 50 mg of pyridoxine for 30 days can correct the static and/or the functional abnormalities of vitamin B6 status seen in patients with rheumatoid arthritis, and further investigate if pyridoxine supplementation has any effects on the pro-inflammatory cytokine TNF-alpha or IL-6 production of arthritis. This was a double-blinded, placebo-controlled study involving patients with rheumatoid arthritis with plasma pyridoxal 5'-phosphate below the 25th percentile of the Framingham Heart Cohort Study. Vitamin B6 status was assessed via plasma and erythrocyte pyridoxal 5'-phosphate concentrations, the erythrocyte aspartate aminotransferase activity coefficient (alphaEAST), net homocysteine increase in response to a methionine load test (DeltatHcy), and 24 h urinary xanthurenic acid (XA) excretion in response to a tryptophan load test. Urinary 4-pyridoxic acid (4-PA) was measured to examine the impact of pyridoxine treatment on vitamin B6 excretion in these patients. Pro-inflammatory cytokine (TNF-alpha and IL-6) production, C-reactive protein levels and the erythrocyte sedimentation rate before and after supplementation were also examined. Pyridoxine supplementation significantly improved plasma and erythrocyte pyridoxal 5'-phosphate concentrations, erythrocyte alphaEAST, urinary 4-PA, and XA excretion. These improvements were apparent regardless of baseline B6 levels. Pyridoxine supplementation also showed a trend (p < 0.09) towards a reduction in post-methionine load DeltatHcy. Supplementation did not affect pro-inflammatory cytokine production. Although pyridoxine supplementation did not suppress pro-inflammatory cytokine production in patients with rheumatoid arthritis, the suboptimal vitamin B6 status seen in rheumatoid arthritis can be corrected by 50 mg pyridoxine supplementation for 30 days. Data from the present study suggest that patients with rheumatoid arthritis may have higher requirements for vitamin B6 than those in a normal healthy population.
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PMID:Pyridoxine supplementation corrects vitamin B6 deficiency but does not improve inflammation in patients with rheumatoid arthritis. 1627 93

Neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD) is a kind of inborn errors of metabolism, with the main clinic manifestations of jaundice, hepatomegaly, and abnormal liver function indices. As a mitochondrial solute carrier protein, citrin plays important roles in aerobic glycolysis, gluconeogenesis, urea cycle, and protein and nucleotide syntheses. Therefore citrin deficiency causes various and complicated metabolic disturbances, such as hypoglycemia, hyperlactic acidemia, hyperammonemia, hypoproteinemia, hyperlipidemia, and galactosemia. This paper reported a case of NICCD confirmed by mutation analysis of SLC25A13, the gene encoding citrin. The baby (male, 6 months old) was referred to the First Affiliated Hospital with the complaint of jaundice of the skin and sclera, which it had suffered from for nearly 6 months. Physical examination showed obvious jaundice and a palpable liver 5 cm below the right subcostal margin. Liver function tests revealed elevated enzymatic activities, like GGT, ALP, AST, and ALT, together with increased levels of TBA, bilirubin (especially conjugated bilirubin), and decreased levels of total protein/albumin and fibrinogen. Blood levels of ammonia, lactate, cholesterol, and triglyceride were also increased, and in particular, the serum AFP level reached 319,225.70 microg/L, a extremely elevated value that has rarely been found in practice before. Tandem mass analysis of a dried blood sample revealed increased levels of free fatty acids and tyrosine, methionine, citrulline, and threonine as well. UP-GC-MS analysis of the urine sample showed elevated galactose and galactitol. The baby was thus diagnosed with suspected NICCD based on the findings. It was then treated with oral arginine and multiple vitamins (including fat-soluble vitamins A, D, E, and K), and was fed with lactose-free and medium-chain fatty acids enriched formula instead of breast feeding. After half a month of treatment, the jaundice disappeared, and the laboratory findings, including liver function indices, blood levels of ammonia, lactate and AFP, were returned to normal level. The baby was followed up for 6 months. It developed well, and the abnormal laboratory findings, including MS-MS and UP-GC-MS analysis results, have been corrected, except a slightly elevated lactate level sometimes. SLC25A13 gene mutation analysis for the patient revealed a compound heterozygote of mutation 851del4 and 1638ins23 and therefore NICCD was definitely diagnosed.
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PMID:[A difficult and complicated case study: neonatal intrahepatic cholestasis caused by citrin deficiency]. 1661 6


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