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PubMed2002

IFCC primary reference procedures for the measurement of catalytic activity concentrations of enzymes at 37 degrees C. International Federation of Clinical Chemistry and Laboratory Medicine. Part 5. Reference procedure for the measurement of catalytic concentration of aspartate aminotransferase.

This paper is the fifth in a series dealing with reference procedures for the measurement of catalytic activity concentrations of enzymes at 37 degrees C and the certification of reference preparations. Other parts deal with: Part 1. The Concept of Reference Procedures for the Measurement of Catalytic Activity Concentrations of Enzymes; Part 2. Reference Procedure for the Measurement of Catalytic Concentration of Creatine Kinase; Part 3. Reference Procedure for the Measurement of Catalytic Concentration of Lactate Dehydrogenase; Part 4. Reference Procedure for the Measurement of Catalytic Concentration of Alanine Aminotransferase; Part 6. Reference Procedure for the Measurement of Catalytic Concentration of Gamma-Glutamyltransferase; Part 7. Certification of Four Reference Materials for the Determination of Enzymatic Activity of Gamma-Glutamyltransferase, Lactate Dehydrogenase, Alanine Aminotransferase and Creatine Kinase at 37 degrees C. A document describing the determination of preliminary upper reference limits is also in preparation. The procedure described here is deduced from the previously described 30 degrees C IFCC reference method. Differences are tabulated and commented on in Appendix 3.

Aspartate Aminotransferases↗
PubMed1992

Aspartate aminotransferase of E. coli: effects of site-directed mutagenesis on substrate recognition.

R292 is crucial for both the binding and the catalysis of the transamination reaction of dicarboxylic acid substrates. Substitution of R292 to uncharged residues greatly enhanced the catalytic efficiency of transamination of neutral amino acids without any effect on the binding. Residues at position 292 may not be involved in recognition of the neutral side chain. The indole ring of W140 not only regulates the rotational movement of the coenzyme ring during catalysis, but it also may be involved in binding the carboxyl side chain of dicarboxylic substrates. The phenol group of Y70 is essential for the stabilization of the transition states with all substrates. Benzene ring at position 70 is necessary to recognize the glutamate-2-oxoglutarate substrate pair.

Amino Acids↗
PubMed2006

[Macro-aspartate aminotransferase in a patient with chronic hepatitis C].

Macroenzymes are normal enzymes complexed with an immunoglobulin (usually IgG, rarely IgA or IgM). A number of macroenzymes have been reported in the literature. Among them, macro-AST has been detected in diseases such as acute and chronic hepatitis, various malignancies and autoimmune diseases, but usually not associated with any specific disease. We report a case of elevated AST activity in serum due to marco-AST formation in a female with chronic hepatitis C which was confirmed by AST isoenzyme electrophoresis. To our knowledge, this is the first report of macro-AST occurred in chronic hepatitis patient in Korea.

Aspartate Aminotransferases↗
PubMed1986

Stereospecific labilization of the C-4' pro-S hydrogen of pyridoxamine 5'-phosphate in aspartate aminotransferase.

In the course of a half-reaction of enzymic transamination, the aldimine adduct formed between the coenzyme pyridoxal 5'-phosphate and the amino acid substrate tautomerizes to the ketimine intermediate which is then hydrolyzed to the oxo acid product and the pyridoxamine 5'-phosphate form of the enzyme. In the reverse half-reaction the tautomerization is initiated by the removal of a proton from the pro-S position at C-4' of the PMP moiety of the ketimine intermediate. The present study investigates the question whether the pro-S hydrogen at C-4' of PMP is labilized by its active site environment independently of the formation of the ketimine intermediate, i.e. in the absence of substrate. Reconstitution of apoaspartate aminotransferase (mitochondrial isoenzyme from chicken) with [4'-3H] PMP results indeed in a stereospecific exchange of pro-S 3H with solvent water. The exchange follows first order kinetics (t 1/2 = 23 min at pH 7.5 and 25 degrees C). Unbound PMP showed no measurable exchange. Rigorous control experiments excluded the possibility that the observed exchange was due to a transamination reaction of the enzyme with contaminating oxo acid substrates. The newly observed stereospecific exchange reaction allows to investigate the acid/base properties of C-4' and the modulating effects of its active site environment independently of the preceding and following steps of enzymic transamination.

Animals↗
PubMed1991

Isoenzyme (lactate dehydrogenase, aspartate aminotransferase) and dipeptidyl peptidase IV activity changes in blood plasma likely indicative of organ involvement due to arterial hypertension.

The plasma activities of LDH and ASAT isoenzymes as well as of DP IV were studied in patients with essential hypertension and related to blood pressure, haemodynamic indicators of latent heart failure and to ischaemic heart risk indicators. Patients with elevated systolic or diastolic blood pressure showed significantly increased activities of ASAT m. In hypertensives with elevated pulmonary artery pressure markedly increased activities of ASAT, ASAT m, LDH M and DP IV could be observed. Distinctly increased activities of ASAT, ASAT m, LDH M and DP IV were also found in patients with elevated plasma cholesterol. The results obtained suggest that changes of LDH and ASAT isoenzymes as well as of DP IV indirectly reflecting alterations in organ metabolism might provide useful additional information with respect to uncovering hypertension-linked complications.

Adult↗
PubMed1975

Aspartate aminotransferase and alanine aminotransferase activities in plasma: statistical distributions, individual variations, and reference values.

The determination of frequency value (percentile limits) and the classification of the different variation factors allow us to define more and more homogeneous subpopulations as we use these factors for sorting. Using as our study population those persons coming to the Centre for Preventive Medicine, we were able to: (a) Describe and measure the significance and importance of physiological variations or of variations attributed to age--the latter largely related only to excessive weight, which it seems to us is often the case. (b) Establish a classification for variation factors; the recapitulatory table should be useful to clinical chemists in helping physicians interpret a laboratory test result that falls within the zone of incertitude. (c) Suggest a preliminary group of reference values for healthy subjects, to be used in interpreting a laboratory test in this way.

Adolescent↗
PubMed1977

[Adaptation on the ABA-100 of the optimized method of measurement of serum aspartate aminotransferase activity].

The analytical modifications necessary for adaptation of the SFBC technic for measurement of the activity of TGO method and those obtained by the technic adapted on ABA 100 suggest that the modifications proposed have no influence on the result of the enzyme estimation. The activation of TGO by addition of its coenzyme was assessed using mathematical models uniting the values of TGO recorded with and without pyridoxal phosphate. It has been shown that the parabolic model is more suitable than the linear model to explain the relation between transaminase activity determined without pyridoxal phosphate and that measured in the presence of the coenzyme. Using estimations carried out in 850 blood donors, it was possible to show that the reference interval of TGO lay between 7 and 28 mUI/ml. In man, the value of TGO is statistically higher than in women. On the other hand between 20 and 60 years there does not seem to be any significant difference depending on age.

Adult↗
PubMed1988

[Altered gamma-glutamyltransferase, aspartate aminotransferase, alanine aminotransferase and alkaline phosphatase serum activities in long-term anticonvulsive therapy--comparison of diphenylhydantoin and carbamazepine].

In 110 patients receiving a long-term anticonvulsant monotherapy with Diphenylhydantoin (DPH) and Carbamazepine (CBZ) the serum activities of gamma-GT, ASAT, ALAT, and AP were examined retrospectively. Elevated serum levels of enzymes were seen predominantly concerning gamma-GT and AP. 91% resp. 39% of patients receiving DPH-therapy showed increased gamma-GT resp. AP-levels compared to 64% and 14% of gamma-GT and AP-elevations by CBZ-treatment. All enzymes evaluated were more often and higher elevated by DPH than CBZ. Frequency and extent of increased activity of gamma-GT were highly related to daily dosage in both preparations. The proportion of pathological enzyme levels was associated with age in DPH and CBZ as well but not found to be significant. Sex differences in the frequency of increased enzyme activities could not be demonstrated. The results are discussed in the context of induction of cytochrome P-450-system.

Adult↗
PubMed1995

Extreme serum elevations of aspartate aminotransferase.

OBJECTIVE: To determine the frequency, etiology, and associated mortality of extreme elevations of serum AST. METHODS: The medical records were reviewed of all patients with a serum AST over 3000 U/L during 1 full calendar year at a large, tertiary-care hospital. Serum AST, with an upper limit of normal at 35 U/L, is included in the automated, 18-test chemistry profile run on virtually all clinically ill patients admitted to this hospital. RESULTS: Of 23,125 admissions, 56 patients had or developed serum AST concentrations greater than 3000 U/L, an occurrence rate of approximately two per 1000 admissions. Either liver or skeletal muscle was the origin of virtually all such AST elevations. Acute hypotension (ischemic or hypoxic hepatitis) accounted for the majority (29/56) of the cases; toxic (seven) or viral (four) hepatitis together accounted for 11/56 cases. Overall mortality, on this admission, was 31/56 (55%). CONCLUSIONS: Extreme elevations of AST are most often attributable to hypoxic hepatitis. Patients with extreme AST due to hypoxic hepatitis had a 22/29 (75%) mortality compared with 9/27 (33%) for all other causes combined.

Academic Medical Centers↗
PubMed1989

Studies on the mechanism of acetaldehyde-mediated inhibition of aspartate aminotransferase (GOT) in human erythrocytes.

The mechanism of acetaldehyde-mediated GOT inhibition was studied in human red cells. In the GOT assay mix, acetaldehyde competitively inhibits activation of apoGOT by pyridoxal phosphate and pyridoxamine phosphate. However, Ki values are 100-1000 times greater than Km values for these B6 vitamers. Moreover, incubation of undiluted lysates with acetaldehyde at 37 degrees inhibits GOT activity without increasing apoGOT levels and without altering affinity of apoGOT for either B6 coenzyme. In undiluted lysates, inhibition is not prevented by disulfiram. However, incubation at 4 degrees prevents both acetaldehyde metabolism and GOT inhibition while preincubation with NaF prevents GOT inhibition without affecting acetaldehyde disappearance. The effect of NaF is completely reversed by pyruvate but only partially reversed by NADH. Glyceraldehyde 3-phosphate, the only glycolytic intermediate which directly inhibits GOT, does not reverse the NaF effect. Thus, inhibition of GOT by acetaldehyde (a) requires nonoxidative metabolism of acetaldehyde and (b) is not mediated either by glycolytic substrates or by impaired binding of B6 vitamers to the GOT apoenzyme. Since NaF had no effect on a lysate deficient in glucose 6-phosphate dehydrogenase, the hexose monophosphate shunt may play a role in acetaldehyde-mediated GOT inhibition.

Acetaldehyde↗
PubMedDate not supplied

[Aspartate aminotransferase (AST) to alanine aminotransferase (ALT) ratio in health surveillance of workers exposed to vinyl chloride monomer: preliminary results].

An AST/ALT ratio > 1 is predictive of liver fibrosis and cirrhosis in patients with chronic hepatitis C virus infection. The aim of this case-control study is to assess AST/ALT ratio in 150 workers exposed to VCM (E) from the beginning of the 1960s to the end of the 1990s. The non-exposed group (NE) consists in 150 male workers employed in the production of a food industry. At least since 1983 exposed subjects worked at VCM environmental concentrations < 3 ppm. All the workers underwent venous blood collection for assessment of AST and ALT. Exposed workers presented mean AST/ALT ratio and frequency of AST/ALT ratio > 1 significantly higher than non-exposed. The mean AST/ALT ratio results significantly higher in the exposed group, also after stratification for alcohol consumption. In exposed workers who consume alcoholic beverages and are operating since before 1983 AST/ALT ratio is significantly and positively influenced only by the working age until 1983. If these results will be confirmed, AST/ALT ratio could be proposed to be included in the periodic medical surveillance of VCM workers.

Adult↗
PubMed1991

[Serum mitochondrial aspartate aminotransferase (ASTm) in acute myocardial infarction].

The increase of serum ASTm activity might reflect the severity of damage at the subcellular level of the myocardium. 50 patients with acute myocardial infarction (AMI) were observed. The mean peak ASTm activity was 34.34 +/- 34.60 IU/L and 48 patients (96%) greater than or equal to 9 IU/L (two times median value of normal subject). The peak time (36 h) came later and the duration (120 h) was longer than that of CK-MB. ASTm/ASTt ratio in groups of AMI, non-AMI heart failure and acute ictero-hepatitis was 0.25 +/- 0.10, 0.02 +/- 0.05 and 0.05 +/- 0.02 respectively. The former was significantly greater than other two groups (P less than 0.01). The activity of ASTm in AMI cases with heart function at I, II and III + IV (Killip classification) was 21.8, 40.2 and 76.2 IU/L respectively (F = 8.407 P less than 0.01) and it was 84.9 and 24.7 IU/L in the death and surviving groups (P less than 0.01). The result showed that the estimation of serum ASTm level was helpful to the establishment of diagnosis in the patients with AMI who were sent delayed to the hospital. It held special significance in evaluating the severity of myocardial damage, heart function and in predicting the prognosis of AMI.

Adult↗
PubMed1986

Prognostic value of mitochondrial aspartate aminotransferase in acute myocardial infarction.

In 112 prospectively selected patients suffering from acute myocardial infarction (AMI), the serum CK, CK-MB, LD, HBD, AST and m-AST were determined from the time of admission to hospital and every 12 hours for three days in succession. Sixteen of the enrolled patients died due to complications which arose within the first four days of hospitalization while the rest had a favourable outcome. All enzyme activities were determined at 37 degrees C using routine methods; m-AST was measured using an immunochemical method. The statistical analysis of the results demonstrated that 12 hours after admission, serum m-AST and m-AST/AST ratio were significantly higher in the group of non-survivors compared with patients with a favourable prognosis. No significant differences in CK-MB were observed between survivors and non-survivors during the entire period. True and false positive rates were calculated for these and the other enzymes. An optimum decision level of 34 IU/L was chosen for m-AST and 10% for the m-AST/AST ratio. This gave a percentage of correctly classified patients, after 12 and 24 hours, of 74.9% and 91.9%, respectively. In conclusion, the immunochemical determination of m-AST in patients with AMI seems to be an early prognostic index which is able to distinguish patients with unfavourable outcome.

Adult↗
PubMed1996

Contribution of a nuclear factor 1 binding site to the glucocorticoid regulation of the cytosolic aspartate aminotransferase gene promoter.

Two regions of the cAspAT gene promoter mediate the glucocorticoid regulation of this gene in the Fao hepatoma cell line. The proximal region was localized by deletion studies and stable transfections in the Fao cells to the sequence -553/-398. This region includes the glucocorticoid-responsive element (GRE) A sequence, which consists of two overlapping GREs and which can mediate the glucocorticoid regulation of a heterologous promoter. DNase I footprinting studies have shown that a site 80 base pairs upstream of the GRE A was protected by liver and brain nuclear extracts (site P8). The binding was displaced by an excess of an oligonucleotide containing a typical NF1 binding site and by NF1-specific antibodies. In electrophoretic mobility shift assay using the P8 oligonucleotide as a probe, several complexes were formed. Most complexes were common to liver and brain but were less abundant when testis extracts were used. At least one complex was specific to the liver. All complexes, with the exception of two, were competed for by the NF1 oligonucleotide. Furthermore, the sequence of the P8 site showed a 7/9-base pair homology with a typical NF1 site. A mutation of the P8 site, which prevents the binding of NF1-like proteins to it, considerably decreases the regulation of the cAspAT promoter fragment by glucocorticoids. Surprisingly, the basal activity of the mutant promoter was increased 2-fold. Thus, the regulation of the cAspAT gene promoter is mediated by a regulatory unit comprising the GRE A and a NF1 binding site.

Animals↗
PubMed1995

The pathogenesis of decreased aspartate aminotransferase and alanine aminotransferase activity in the plasma of hemodialysis patients: the role of vitamin B6 deficiency.

The mechanisms responsible for the low plasma (p) AST and ALT activity in HD patients remain elusive. This prospective study was undertaken to clarify the relationship of AST, ALT and pyridoxal-5'-phosphate (PLP) levels (active form of vitamin B6) in these patients. A group of 52 HD patients were given oral pyridoxine HCl (30 mg daily), for 5 weeks. Prior to supplementation (Day 0), 17 (33%) patients had deficient pPLP levels (Group 1), the remainder (35 patients) had normal pPLP values (Group 2). A positive correlation was noted between pPLP and pAST (r = 0.57, p < 0.01) or pALT (r = 0.68, p < 0.01). The mean pAST (9.2 +/- 0.3 vs 13.4 +/- 0.7 U/l) and pALT (8.6 +/- 0.6 vs 11.4 +/- 0.9 U/l) were markedly lower in Group 1 than those in Group 2, respectively. These low AST and ALT levels increased to those seen in Group 2 where no change from basal values was seen despite vitamin B6 supplementation (Day 35). The administration of vitamin B6 resulted in a significant increase in pPLP in both groups (Day 35) but pPLP dropped to subnormal levels in 5 patients in Group 1 and 7 in Group 2 three months after supplementation was stopped (Day 125). The mean AST and ALT of these 12 pPLP deficient patients became lower than those of the remaining 40 patients with normal pPLP values (p < 0.05). In conclusion, low pAST and pALT levels in HD patients are in part due to a deficiency of pPLP which serves as a coenzyme for these transaminases.

Adult↗
PubMed1991

Hepatic activity and mRNA expression of aspartate aminotransferase isoenzymes in alcoholic and nonalcoholic liver disease.

In liver and serum, AST activity is dependent on two isoenzymes, which are mitochondrial and cytosolic in nature. In an attempt to explain the well-known increase of serum mitochondrial AST-to-total AST ratio in chronic alcoholism (which is due to a specific increase of the mitochondrial isoenzyme), we analyzed: (a) liver and serum AST, ALT and glutamate dehydrogenase activities in 23 active drinkers with minimal liver changes, 11 alcoholic patients with cirrhosis who had stopped drinking, 18 nonalcoholic patients with viral chronic hepatitis and 11 subjects with normal livers; and (b) the expression of messenger RNAs for AST isoenzymes in the corresponding liver samples. Enzymatic activities were decreased in the liver irrespective of the origin of the liver disease. In patients with viral chronic hepatitis (or in those with alcoholic cirrhosis when abstinent), variations in liver proteins and messenger RNAs paralleled significant decreases in mitochondrial AST, ALT and glutamate dehydrogenase and a nonsignificant decrease of cytosolic AST. In alcoholic patients with minimal liver changes, the significant decrease of hepatic cytosolic AST, ALT and glutamate dehydrogenase activities contrasted with a close-to-normal liver mitochondrial AST activity; the increased amounts of mitochondrial AST messenger RNA give evidence for a pretranslational mechanism of regulation, indicating a possible increase in the total production of mitochondrial AST in the liver. The decrease of hepatic cytosolic AST activity was statistically significant only in alcoholic patients without cirrhosis who had a normal cytosolic AST mRNA level, thus suggesting a contributory role of translational or posttranslational regulation. In conclusion, regulation of AST isozymes during liver disease is complex, including differential, pretranslational and translational or posttranslational mechanisms.

Aspartate Aminotransferases↗
PubMed2002

[Aspartate aminotransferase (AST) more than alanine aminotransferase (ALT) levels predict the progression of liver fibrosis in chronic HCV infection].

The development and severity of liver fibrosis in patients with chronic HCV infection can be evaluated best according to the staging of fibrosis in blind liver biopsy. So far there is however no biochemical indicator suggesting advanced fibrosis or progression of fibrosis in chronic HCV infection. In 1997 - 1999 60 adult out-patients (32 women) with chronic HCV infection were examined by blind liver biopsy. The grading of hepatitis was scored according to Knodell and staging of fibrosis according to Desmet. All patients were anti-HCV positive, assessed by the ELISA-3 method and 48/60 had positive HCV RNA in serum. The main risk factor of HCV infection was blood transfusion (67%). Of 27 examined patients 20 (74%) had serotype HCV 1. Staging of fibrosis: histologically confirmed fibrosis was not recorded in 11 patients (18.3%), mild and medium fibrosis was recorded in 25 (42%), severe fibrosis in 14 (23%) and cirrhosis in 10 (17%). With confirmed fibrosis correlated more closely AST serum activity (p < 0.002) than ALT activity (p < 0.03). Steatosis of the liver was found in 25 (42%) patients. The mean age of patients with steatosis was significantly higher than that of patients without steatosis (p < 0.0008). Steatosis was more frequent in patients with fibrosis (p < 0.04), in particularin the age group above 60 years. The development of fibrosis in patients with chronic HCV infection is suggested by permanently elevated activity of both transaminases whereby AST has a higher predictive value than ALT activity. A total of 40% histologically tested patients had the highest staging of fibrosis (3 - 4). Steatosis is in chronic HCV infection a very frequent finding (42%), in particular in patients above 60 years and those with serious fibrosis. The finding of fibrosis should stimulate the initiation of antiviral treatment which can lead to regression of fibrosis and improvement of the histological finding.

Adolescent↗
PubMed1978

Fluorescence of aromatic amino acids in a pyridoxal phosphate enzyme: aspartate aminotransferase.

At pH 8.3, the fluorescence spectrum of apoaspartate aminotransferase is characteristic of buried tryptophans (maximum at 330 nm and width at half-height equal to 51 nm). Its quantum yield is 1.69 times larger than for tryptophan in H2O and the mean decay time is 2.5 ns for the fluorescence emitted at wavelengths higher than 335 nm. Polarization of excitation spectrum (minimum at 305 nm for an emission at 360 nm), suggests an inter-tryptophan energy transfer. Accessibility to a quencher of fluorescence indicates that 34% of the fluorescence can be extinguished by iodide with a quenching constant of 4 M-1; as shown by solvent perturbation spectroscopy, this partial accessibility is related to two tryptophan residues accessible to solvent. At pH 5, the relative quantum yield is slightly lower than at pH 8.3 (1.65). Binding of the pyridoxal-P coenzyme diminishes the fluorescence quantum yield relative to tryptophan to 0.51 at pH 8.3 and 0.595 at pH 5; the decrease is smaller in the presence of pyridoxamine-P. Since the fluorescence of the coenzyme is very weak it is difficult to observe its emission sensitized by tryptophan, nevertheless, since the quenching is larger for pyridoxal-P that absorbs at 360 nm than for reduced pyridoxal-P that absorbs at 330 nm, it is deduced that the energy is transferred preferentially from exposed tryptophans. It is proposed that conformational changes in the vicinity of buried tryptophans are responsible for the remaining quenching. This hypothesis of conformational changes induced by the binding of the coenzyme is in agreement with the observed fluorescence emission of tyrosine. In the apoenzyme the tyrosine quantum yield is zero and the energy is entirely transferred to tryptophan. In the holoenzyme the quantum yield is low and the efficiency of transfer to tryptophan is 0.13 in pyridoxal-P form and 0.7 in pyridoxamine-P form. According to the Förster theory of long-range energy transfer, a change of transfer efficiency can be attributed to a modification either of the mutual orientation of tyrosine and tryptophan residues or of the distance between these residues: both interpretations correspond to a conformational change.

Animals↗