Further thermal characterization of an aspartate aminotransferase from a halophilic organism.
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ABSTRACT:
SUBMITTER: Muriana FJ
PROVIDER: S-EPMC1137963 | biostudies-other | 1994 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.
| S-EPMC3046307 | biostudies-literature
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: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: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:BackgroundThe prognostic significance of the aspartate aminotransferase/alanine aminotransferase (AST/ALT) ratio in hepatocellular carcinoma remains uncertain. The aim of the current study was to evaluate the association between the AST/ALT ratio and prognosis in patients with hepatocellular carcinoma after hepatectomy, and to explore the role of underlying liver diseases as mediators.MethodsThis retrospective study included patients with hepatocellular carcinoma who underwent hepatectomy between January 2014 and January 2018 at two Chinese hospitals. The maximally selected rank statistic and g-computation approach were used to quantify and visualize the association between the AST/ALT ratio and overall survival or recurrence-free survival. The role of mediators (chronic hepatitis B, hepatic steatosis and liver cirrhosis) was analysed.ResultsAmong the 1519 patients (mean(s.d.) age at baseline, 50.5(11.3) years), 1309 (86.2%) were male. During a median follow-up of 46.0 months, 514 (33.8%) patients died and 358 (23.6%) patients experienced recurrence. The optimal cut-off value for the AST/ALT ratio was 1.4, and the AST/ALT ratio greater than or equal to 1.4 was independently associated with a 39.0% increased risk of death and a 30.0% increased risk of recurrence (overall survival: hazard ratio (HR), 1.39; 95% c.i. 1.15 to 1.68; recurrence-free survival: HR, 1.30; 95% c.i. 1.12 to 1.52) after adjusting for confounders. Chronic hepatitis B significantly mediated the association of the ratio of AST/ALT with both overall survival and recurrence-free survival (20.3% for overall survival; 20.1% for recurrence-free survival).ConclusionThe AST/ALT ratio greater than or equal to 1.4 was associated with shorter overall survival and recurrence-free survival in patients with hepatocellular carcinoma after hepatectomy, and chronic hepatitis B may play a role in their association.
| S-EPMC10798825 | biostudies-literature
Project description:Aspartate aminotransferases have been cloned and expressed from Crithidia fasciculata, Trypanosoma brucei brucei, Giardia intestinalis, and Plasmodium falciparum and have been found to play a role in the final step of methionine regeneration from methylthioadenosine. All five enzymes contain sequence motifs consistent with membership in the Ia subfamily of aminotransferases; the crithidial and giardial enzymes and one trypanosomal enzyme were identified as cytoplasmic aspartate aminotransferases, and the second trypanosomal enzyme was identified as a mitochondrial aspartate aminotransferase. The plasmodial enzyme contained unique sequence substitutions and appears to be highly divergent from the existing members of the Ia subfamily. In addition, the P. falciparum enzyme is the first aminotransferase found to lack the invariant residue G197 (P. K. Mehta, T. I. Hale, and P. Christen, Eur. J. Biochem. 214:549-561, 1993), a feature shared by sequences discovered in P. vivax and P. berghei. All five enzymes were able to catalyze aspartate-ketoglutarate, tyrosine-ketoglutarate, and amino acid-ketomethiobutyrate aminotransfer reactions. In the latter, glutamate, phenylalanine, tyrosine, tryptophan, and histidine were all found to be effective amino donors. The crithidial and trypanosomal cytosolic aminotransferases were also able to catalyze alanine-ketoglutarate and glutamine-ketoglutarate aminotransfer reactions and, in common with the giardial aminotransferase, were able to catalyze the leucine-ketomethiobutyrate aminotransfer reaction. In all cases, the kinetic constants were broadly similar, with the exception of that of the plasmodial enzyme, which catalyzed the transamination of ketomethiobutyrate significantly more slowly than aspartate-ketoglutarate aminotransfer. This result obtained with the recombinant P. falciparum aminotransferase parallels the results seen for total ketomethiobutyrate transamination in malarial homogenates; activity in the latter was much lower than that in homogenates from other organisms. Total ketomethiobutyrate transamination in Trichomonas vaginalis and G. intestinalis homogenates was extensive and involved lysine-ketomethiobutyrate enzyme activity in addition to the aspartate aminotransferase activity. The methionine production in these two species could be inhibited by the amino-oxy compounds canaline and carboxymethoxylamine. Canaline was also found to be an uncompetitive inhibitor of the plasmodial aspartate aminotransferase, with a K(i) of 27 microm.
| S-EPMC95336 | biostudies-literature
Project description:There have been no reports on mortality in patients with markedly elevated aspartate aminotransferase (AST) levels from non-hepatic causes to date. This study aimed to determine the etiologies of markedly elevated AST levels > 400 U/L due to non-hepatic causes and to investigate the factors associated with mortality in these cases. This retrospective study included 430 patients with AST levels > 400 U/L unrelated to liver disease at two centers between January 2010 and December 2021. Patients were classified into three groups according to etiology: skeletal muscle damage, cardiac muscle damage, and hematologic disorder. Binary logistic regression analysis was performed to evaluate the factors associated with 30-day mortality. The most common etiology for markedly elevated AST levels was skeletal muscle damage (54.2%), followed by cardiac muscle damage (39.1%) and hematologic disorder (6.7%). The 30-day mortality rates for the skeletal muscle damage, cardiac muscle damage, and hematologic disorder groups were 14.2%, 19.5%, and 65.5%, respectively. The magnitude of the peak AST level significantly correlated with 30-day mortality, with rates of 12.8%, 26.7%, and 50.0% for peak AST levels < 1000 U/L, <3000 U/L, and ≥3000 U/L, respectively. In the multivariate analysis, cardiac muscle damage (odds ratio [OR] = 2.76, 95% confidence interval [CI] = 1.31-5.80), hematologic disorder (OR = 9.47, 95% CI = 2.95-30.39), peak AST < 3000 U/L (OR = 2.94, 95% CI = 1.36-6.35), and peak AST ≥ 3000 U/L (OR = 9.61, 95% CI = 3.54-26.08) were associated with increased 30-day mortality. Our study revealed three etiologies of markedly elevated AST unrelated to liver disease and showed that etiology and peak AST level significantly affected the survival rate.
| S-EPMC9821092 | biostudies-literature
Project description:BackgroundFew studies discussed the predictive ability of aspartate aminotransferase/alanine aminotransferase (AST/ALT, DeRitis) ratio for diabetes risk. The aim of this study was to characterize the role of AST/ALT ratio in the prediction of Chinese diabetes.MethodsThis retrospective cohort study analyzed a Chinese population comprising 87,883 participants without diabetes at baseline between 2010 and 2016. Cox proportional hazards regression was used to identify independent risk factors. Restricted cubic spline (RCS) was performed to investigate the non-linear correlation between AST/ALT ratio and diabetes risk.ResultsDuring a median follow-up period of 3.01 years, 1,877 participants developed diabetes. Comparing the baseline characteristics, diabetes group exhibited lower AST/ALT ratio. The Kaplan-Meier curve showed that participants with low AST/ALT ratio had higher cumulative incidence, and Cox regression also demonstrated that the lower AST/ALT ratio, the higher diabetes risk (HR: 0.56, 95% CI: 0.37-0.85, P = 0.006). The RCS model revealed a non-linear correlation between AST/ALT ratio and diabetes risk. In the condition of AST/ALT ratio ≤1.18, diabetes risk increased as it decreased (HR: 0.42, 95% CI: 0.19-0.91, P = 0.028). In contrast, AST/ALT ratio did not independently affect diabetes when beyond 1.18.ConclusionAST/ALT ratio is a valuable predictor of diabetes. Diabetes risk increases rapidly in the condition of AST/ALT ratio ≤1.18.
| S-EPMC9666731 | biostudies-literature
Project description:The mechanisms of pyridoxal 5'-phosphate (PLP)-dependent enzymes require substrates to form covalent "external aldimine" intermediates, which absorb light strongly between 410 and 430 nm. Aspartate aminotransferase (AAT) is a prototypical PLP-dependent enzyme that catalyzes the reversible interconversion of aspartate and ?-ketoglutarate with oxalacetate and glutamate. From kinetic isotope effects studies, it is known that deprotonation of the aspartate external aldimine C(?)-H bond to give a carbanionic quinonoid intermediate is partially rate limiting in the thermal AAT reaction. We show that excitation of the 430-nm external aldimine absorption band increases the steady-state catalytic activity of AAT, which is attributed to the photoenhancement of C(?)-H deprotonation on the basis of studies with Schiff bases in solution. Blue light (250 mW) illumination gives an observed 2.3-fold rate enhancement for WT AAT activity, a 530-fold enhancement for the inactive K258A mutant, and a 58600-fold enhancement for the PLP-Asp Schiff base in water. These different levels of enhancement correlate with the intrinsic reactivities of the C(?)-H bond in the different environments, with the less reactive Schiff bases exhibiting greater enhancement. Time-resolved spectroscopy, ranging from femtoseconds to minutes, was used to investigate the nature of the photoactivation of C(?)-H bond cleavage in PLP-amino acid Schiff bases both in water and bound to AAT. Unlike the thermal pathway, the photoactivation pathway involves a triplet state with a C(?)-H pK(a) that is estimated to be between 11 and 19 units lower than the ground state for the PLP-Val Schiff base in water.
| S-EPMC3021986 | biostudies-literature
Project description:Liver disease is a common comorbid condition in maintenance hemodialysis (MHD) patients and may be associated with poor survival. The relationship between aspartate aminotransferase (AST) and survival has not yet been addressed in these patients. We hypothesized that higher AST level is associated with higher death risk in MHD patients.A 5-year (January 2007-December 2011) cohort of 109 718 MHD patients was studied in the USA in dialysis clinics where AST was measured in at least 50% of all outpatients in the baseline calendar quarter. Survival models were adjusted for demographic variables, and available clinical and laboratory surrogates of malnutrition-inflammation complex, and cubic survival splines were plotted.A linear association existed between baseline serum AST levels and mortality. Increasing AST of >20 IU/L was incrementally and almost linearly associated with higher death risk at all levels of adjustment. In fully adjusted models, AST levels of ?40 IU/L were associated with the highest risk of mortality (hazard ratio: 1.46, 95% CI: 1.38-1.54). Low AST levels (<15 IU/L) were associated with increased death risk only in fully adjusted models examining hepatitis C virus-positive patients.Higher AST level of >20 IU/L is incrementally associated with higher mortality in MHD patients whereas AST in the 15-20 IU/L range is associated with the greatest survival. These findings suggest that the assessment of liver function and improving liver disease may confer survival benefit to MHD patients.
| S-EPMC4848754 | biostudies-literature