Kinetic studies of chicken and turkey liver mitochondrial aspartate aminotransferase.
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ABSTRACT:
SUBMITTER: Cascante M
PROVIDER: S-EPMC1148927 | biostudies-other | 1988 Mar
REPOSITORIES: biostudies-other
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Project description:Mammalian mAspAT (mitochondrial aspartate aminotransferase) is recently reported to have KAT (kynurenine aminotransferase) activity and plays a role in the biosynthesis of KYNA (kynurenic acid) in rat, mouse and human brains. This study concerns the biochemical and structural characterization of mouse mAspAT. In this study, mouse mAspAT cDNA was amplified from mouse brain first stand cDNA and its recombinant protein was expressed in an Escherichia coli expression system. Sixteen oxo acids were tested for the co-substrate specificity of mouse mAspAT and 14 of them were shown to be capable of serving as co-substrates for the enzyme. Structural analysis of mAspAT by macromolecular crystallography revealed that the cofactor-binding residues of mAspAT are similar to those of other KATs. The substrate-binding residues of mAspAT are slightly different from those of other KATs. Our results provide a biochemical and structural basis towards understanding the overall physiological role of mAspAT in vivo and insight into controlling the levels of endogenous KYNA through modulation of the enzyme in the mouse brain.
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Project description:BACKGROUND/AIMS:Enzymatic analysis of aspartate/alanine aminotransferase (AST/ALT) does not exactly represent the progression of liver fibrosis or inflammation. Immunoassay for AST (cytoplasmic [c] AST/mitochondrial [m] AST) and ALT (ALT1/ALT2) has been suggested as one alternatives for enzymatic analysis. The objective of this study was to evaluate the efficacy of immunoassay in predicting liver fibrosis and inflammation. METHODS:A total of 219 patients with chronic hepatitis B (CHB) who underwent hepatic venous pressure gradient (HVPG) and liver biopsy before antiviral therapy were recruited. Serum samples were prepared from blood during HVPG. Results of biochemical parameters including enzymatic AST/ALT and immunological assays of cAST, mAST, ALT1, and ALT2 through sandwich enzyme-linked immunosorbent assay (ELISA) immunoassay with fluorescence labeled monoclonal antibodies were compared with the results of METAVIR stage of live fibrosis and the Knodell grade of inflammation. RESULTS:METAVIR fibrosis stages were as follows: F0, six (3%); F1, 52 (24%); F2, 88 (40%); F3, 45 (20%); and F4, 28 patients (13%). Mean levels of AST and ALT were 121 ± 157 and 210 ± 279 IU/L, respectively. Mean HVPG score of all patients was 4.7 ± 2.5 mmHg. According to the stage of liver fibrosis, HVPG score (p < 0.001, r = 0.439) and ALT1 level (p < 0.001, r = 0.283) were significantly increased in all samples from patients with CHB. ALT (p < 0.001, r = 0.310), ALT1 (p < 0.001, r = 0.369), and AST (p < 0.001, r = 0.374) levels were positively correlated with Knodell grade of inflammation. CONCLUSION:ALT1 measurement by utilizing sandwich ELISA immunoassay can be useful method for predicting inf lammation grade and fibrosis stage in patients with CHB.
| S-EPMC7060995 | biostudies-literature
Project description:Kinetic measurements of the uptake of native mitochondrial aspartate aminotransferase and malate dehydrogenase into mitochondria in vitro were carried out. The uptake of both the enzymes is essentially complete in 1 min and shows saturation characteristics. The rate of uptake of aspartate aminotransferase into mitochondria is decreased by malate dehydrogenase, and vice versa. The inhibition is exerted by isoenzyme remaining outside the mitochondria rather than by isoenzyme that has been imported. The thiol compound beta-mercaptoethanol decreases the rate of uptake of the tested enzymes; inhibition is a result of interaction of beta-mercaptoethanol with the mitochondria and not with the enzymes themselves. The rate of uptake of aspartate aminotransferase is inhibited non-competitively by malate dehydrogenase, but competitively by beta-mercaptoethanol. The rate of uptake of malate dehydrogenase is inhibited non-competitively by aspartate aminotransferase and by beta-mercaptoethanol. beta-Mercaptoethanol prevents the inhibition of the rate of uptake of malate dehydrogenase by aspartate aminotransferase. These results are interpreted in terms of a model system in which the two isoenzymes have separate but interacting binding sites within a receptor in the mitochondrial membrane system.
| S-EPMC1145008 | biostudies-other
Project description:BackgroundWe aimed to evaluate the association between the aspartate aminotransferase (AST)/alanine aminotransferase (ALT) ratio and subsequent development of any type of cancer in an apparently healthy population.MethodsWe conducted a retrospective cohort study at St. Luke's International Hospital, Tokyo, Japan between 2005 and 2018. All participants who visited for voluntary health checkups were included. We divided the participants into different quintiles based on the baseline AST/ALT ratios and examined the outcomes.ResultsA total of 85,658 participants were included. The mean age was 44.7 years (standard deviation 12.0) at baseline, and 42,913 (50.1%) of them were men. During a median follow-up of 61.6 months, 4701 (5.5%) participants developed some type of cancer. Compared with the middle AST/ALT ratio group, no other groups had similar adjusted hazard ratios (HR) for the development of any type of cancer in both men and women. When stratified by alcohol consumption, very high (adjusted HR 1.36; 95% CI 1.13-1.63) and high (adjusted HR 1.26; 95% CI 1.05-1.50) AST/ALT ratio groups among men who were regular drinkers had increased adjusted HRs for any type of cancer development, but the very high AST/ALT ratio group among men who were abstainers (adjusted HR 0.64; 95% CI 0.42-0.97) and very low AST/ALT ratio group among men who were occasional drinkers (adjusted HR 0.69; 95% CI 0.48-0.98) had lower adjusted HRs compared with the middle AST/ALT ratio group. Among women, regardless of alcohol consumption, adjusted HR for any type of cancer development was similar across all AST/ALT ratio groups.ConclusionPeople with higher AST/ALT ratios tended to have a higher risk of developing any type of cancer among men who were regular drinkers, but this risk was lower among men who were abstainers. Among women, regardless of alcohol consumption, there was no association between the development of any type of cancer and AST/ALT ratio.
| S-EPMC8817090 | biostudies-literature
Project description:A method for the purification of mitochondrial isoenzyme of sheep liver aspartate aminotransferase (EC 2.6.1.1) is described. The final preparation is homogeneous by ultracentrifuge analyses and polyacrylamide-gel electrophoresis and has a high specific activity (182 units/mg). The molecular weight determined by sedimentation equilibrium is 87,100 +/- 680. The amino acid composition is presented; it is similar to that of other mitochondrial isoenzymes, but with a higher content of tyrosine and threonine. Subforms have been detected. On isoelectric focusing a broad band was obtained, with pI 9.14. The properties of the mitochondrial aspartate aminotransferase are compared with those of the cytoplasmic isoenzyme. The Km for L-aspartate and 2-oxoglutarate for the cytoplasmic enzyme were 2.96 +/- 0.20 mM and 0.093 +/- 0.010 mM respectively; the corresponding values for the mitochondrial form were 0.40 +/- 0.12 mM and 0.98 +/- 0.14 mM. Cytoplasmic aspartate aminotransferase showed substrate inhibition by concentrations of 2-oxoglutarate above 0.25 mM in the presence of aspartate up to 2mM. The mitochondrial isoenzyme was not inhibited in this way. Pi at pH 7.4 inhibited cytoplasmic holoenzyme activity by up to about 60% and mitochondrial holoenzyme activity up to 40%. The apparent dissociation constants for pyridoxal 5'-phosphate were 0.23 micrometer (cytoplasmic) and 0.062 micrometer (mitochondrial) and for pyridoxamine 5'-phosphate they were 70 micrometer (cytoplasmic) and 40 micrometer (mitochondrial). Pi competitively inhibited coenzyme binding to the apoenzymes; the inhibition constants at 37 degree C were 32 micrometer for the cytoplasmic isoenzyme and 19.5 micrometer for the mitochondrial form.
| S-EPMC1186409 | biostudies-other
Project description:The dynamic aspartate-to-alanine aminotransferase ratio (dAAR) was developed recently to predict the risk of incident chronic liver disease among the Nordic adult population; however, the dAAR has not been externally validated in other ethnic cohorts. Therefore, we aimed to examine the predictive ability of dAAR for liver disease mortality in the South Korean adult population. As a population-based cohort study, we used the National Health Screening Cohort database, which included adult individuals who underwent standardized medical examinations between 2002 and 2003 in South Korea. The primary endpoint was liver disease mortality, defined as death due to liver disease. Liver disease mortality was evaluated between 2004 and 2015 (12 years). Analysis of data from 512,749 adults showed that 4,052 (0.8%) individuals died due to liver disease. On receiver operating characteristic (ROC) analyses, the area under curve for alanine aminotransferase (ALT), aspartate-to-ALT ratio (AAR), and dAAR for liver disease mortality were 0.74, 0.55, and 0.81, respectively. The cutoff point of dAAR was determined to be 0.72 on ROC analysis, using the Youden index method. On competing risk analysis using the Fine and Gray model, the dAAR > 0.72 group demonstrated a 4.43-fold higher rate of liver disease mortality (subdistribution hazard ratio: 4.43, 95% confidence interval: 4.11, 4.77; P < 0.001) after adjustment for covariates. Conclusion: The performance of dAAR in predicting liver disease mortality was better than that of AAR or ALT in South Korea. Our study suggests that dAAR scores can potentially be used for screening and predicting liver disease mortality among the general Korean population.
| S-EPMC8948584 | biostudies-literature
Project description:Gene rv3722c of Mycobacterium tuberculosis is essential for in vitro growth, and encodes a putative pyridoxal phosphate-binding protein of unknown function. Here we use metabolomic, genetic and structural approaches to show that Rv3722c is the primary aspartate aminotransferase of M. tuberculosis, and mediates an essential but underrecognized role in metabolism: nitrogen distribution. Rv3722c deficiency leads to virulence attenuation in macrophages and mice. Our results identify aspartate biosynthesis and nitrogen distribution as potential species-selective drug targets in M. tuberculosis.
| S-EPMC7181641 | biostudies-literature
Project description:The aspartate-to-alanine aminotransferase ratio (AAR) is associated with liver fibrosis, but its predictive performance is suboptimal. We hypothesized that the association between AAR and liver disease depends on absolute transaminase levels and developed and validated a model to predict liver-related outcomes in the general population. A Cox regression model based on age, AAR, and alanine aminotransferase (ALT) level (dynamic AAR [dAAR]) using restricted cubic splines was developed in Finnish population-based health-examination surveys (FINRISK, 2002-2012; n = 18,067) with linked registry data for incident liver-related hospitalizations, hepatocellular carcinoma, or liver death. The model was externally validated for liver-related outcomes in a Swedish population cohort (Swedish Apolipoprotein Mortality Risk [AMORIS] subcohort; n = 126,941) and for predicting outcomes and/or prevalent fibrosis/cirrhosis in biopsied patients with nonalcoholic fatty liver disease (NAFLD), chronic hepatitis C, or alcohol-related liver disease (ALD). The dynamic AAR model predicted liver-related outcomes both overall (optimism-corrected C-statistic, 0.81) and in subgroup analyses of the FINRISK cohort and identified persons with >10% risk for liver-related outcomes within 10 years. In independent cohorts, the C-statistic for predicting liver-related outcomes up to a 10-year follow-up was 0.72 in the AMORIS cohort, 0.81 in NAFLD, and 0.75 in ALD. Area-under-the-curve (AUC) for detecting prevalent cirrhosis was 0.80-0.83 in NAFLD, 0.80 in hepatitis C, but only 0.71 in ALD. In ALD, model performance improved when using aspartate aminotransferase instead of ALT in the model (C-statistic, 0.84 for outcome; AUC, 0.82 for prevalent cirrhosis). Conclusion: A dAAR score provides prospective predictions for the risk of incident severe liver outcomes in the general population and helps detect advanced liver fibrosis/cirrhosis. The dAAR score could potentially be used for screening the unselected general population and as a trigger for further liver evaluations.
| S-EPMC8183175 | biostudies-literature
Project description:Mitochondrial aspartate aminotransferase is inactivated irreversibly on heating. The inactivated protein aggregates, but aggregation is prevented by the presence of the chaperonin 60 from Escherichia coli (GroEL). The chaperonin increases the rate of thermal inactivation in the temperature range 55-65 degrees C but not at lower temperatures. It has previously been shown [Twomey and Doonan (1997) Biochim. Biophys. Acta 1342, 37-44] that the enzyme switches to a modified, but catalytically active, conformation at approx. 55-60 degrees C and the present results show that this conformation is recognized by and binds to GroEL. The thermally inactivated protein can be released from GroEL in an active form by the addition of chaperonin 10 from E. coli (GroES)/ATP, showing that inactivation is not the result of irreversible chemical changes. These results suggest that the irreversibility of thermal inactivation is due to the formation of an altered conformation with a high kinetic barrier to refolding rather than to any covalent changes. In the absence of chaperonin the unfolded molecules aggregate but this is a consequence, rather than the cause, of irreversible inactivation.
| S-EPMC1219682 | biostudies-other
Project description:Rat liver mitochondrial aspartate aminotransferase (a homodimer) was shown to catalyse a beta-lyase reaction with three nephrotoxic halogenated cysteine S-conjugates [ S -(1,1,2,2-tetrafluoroethyl)-L-cysteine, S -(1,2-dichlorovinyl)-L-cysteine and S -(2-chloro-1,1,2-trifluoroethyl)-L-cysteine], and less effectively so with a non-toxic cysteine S-conjugate [benzothiazolyl-L-cysteine]. Transamination competes with the beta-lyase reaction, but is not favourable. The ratio of beta elimination to transamination in the presence of S -(1,1,2,2-tetrafluoroethyl)-L-cysteine and 2-oxoglutarate is >100. Syncatalytic inactivation by the halogenated cysteine S-conjugates is also observed. The enzyme turns over approx. 2700 molecules of halogenated cysteine S-conjugate on average for every monomer inactivated. Kidney mitochondria are known to be especially sensitive to toxic halogenated cysteine S-conjugates. Evidence is presented that 15-20% of the cysteine S-conjugate beta-lyase activity towards S -(1,1,2,2-tetrafluoroethyl)-L-cysteine in crude kidney mitochondrial homogenates is due to mitochondrial aspartate aminotransferase. The possible involvement of mitochondrial aspartate aminotransferase in the toxicity of halogenated cysteine S-conjugates is also discussed.
| S-EPMC1222959 | biostudies-other