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At least 865 records · Page 48Linked to original sources

PubMed2002

Identification of L-glutamine: 2-deoxy-scyllo-inosose aminotransferase required for the biosynthesis of butirosin in Bacillus circulans.

Using inverse PCR, two new genes (btrN and btrS) were identified upstream of the putative glycosyltransferase gene btrM in the butirosin-biosynthetic btr gene cluster of Bacillus circulans. The upstream gene btrS showed significant homology with stsC of Streptomyces griseus, which encodes L-glutamine:scyllo-inosose aminotransferase in the biosynthesis of streptomycin. The function of BtrS was further confirmed by heterologous expression in Escherichia coli and chemical identification of the conversion of 2-deoxy-scyllo-inosose into 2-deoxy-scyllo-inosamine. The identification of BtrS as L-glutamine:2-deoxy-scyllo-inosose aminotransferase is the first report of the aminotransferase gene responsible for 2-deoxystreptamine biosynthesis.

Amino Acid Sequence↗

PubMed1978

In vitro studies of the effect of metal ions, EDTA and their mixtures on kynurenine aminotransferase and kynurenine hydrolase.

In the present study use was made of the chelating ability of EDTA and the activating property of some metal ions Ca(II), Mg(II) or Mn(II) to counteract the inhibitory effect of Cu(II), Co(II), Pb(II) or Zn(II) ions on the B6-dependent kynurenine hydrolase and on kynurenine aminotransferase. These may be of help in studying the therapeutic trials in the treatment of metal poisoning. EDTA was able to counteract the inhibitory effect of Cu(II) or Co(II) on kynurenine aminotransferase and partially counteract the inhibitory effect of Cu(II), Co(II) on kynurenine aminotransferase and partially counteract the inhibitory effect of Cu(II), Co(II), Pb(II) or Zn(II) ions on kynurenine hydrolase. The difference in the response of the two B6-dependent enzymes to EDTA is attributed to the difference in the functional groups involved in the active site(s) of the two apoenzymes. Moreover, Mn(II), Ca(II) and Mg(II) ions have the ability to counteract some of the inhibitory effect of these metal ions.

Animals↗

PubMed1992

Tyrosine aminotransferase: a transaminase among others?

Tyrosine aminotransferase (L-tyrosine: 2 oxoglutarate aminotransferase; EC 2.6.1.5; TATase) is the first enzyme in the catabolic pathway of tyrosine. The gene of this transaminase is regulated by glucocorticoid hormones as well as via the cAMP pathway. This review gives a brief survey of the structural and physico-chemical properties of this well-known protein. A comparative study of the properties of TATase with other aminotransferases is also included to analyse this molecule for itself, and not only as a marker used in studies on enzymatic induction. Finally, the regulation of the gene expression is presented, in order to underline a few important features of this model.

Amino Acid Sequence↗

PubMed1992

[The effect of acute poisoning of rats with carbaryl on the transamination reactions involving alpha-ketoglutarate. Part I. Activity of plasma aminotransferases].

White male Wistar rats were poisoned orally with a single carbaryl dose 474 mg/kg (1/2 LD50). In the plasma of control animals and 2, 4, 24 and 72 hours after administration of the insecticide the activity of aminotransferase catalysing the reactions between alpha-ketoglutarate and six amino acids (cysteine, lysine, phenylalanine, leucine, asparagine and valine) was determined. Aminotransferases activity was expressed as the amount of glutamic acid developing during incubation of 1 cm3 of plasma for 1 hour. Glutamic acid was determined spectrophotometrically after chromatographic separation on paper. The results of the investigations demonstrated that acute intoxication with carbaryl caused a statistically significant increase in the activity of two aminotransferases in the plasma of experimental animals. A rise in the activity of the enzyme catalysing the reaction between alpha-ketoglutarate and asparagine ketoglutarate and lysine was observed.

Animals↗

PubMed1977

Kinetics of the alanine aminotransferase reaction in the mitochondrial and cell sap fractions of rat brain.

1. A reversible transamination reaction between L-glutamate and pyruvate, or L-alanine and 2-oxoglutarate, takes place in the mitochondrial and cell sap fractions of rat brain. 2. The maximum rate of the transamination reaction in both subfractions was observed in the presence of a keto- substrate concentration of 2.5 mM only, but an amino- donor concentration of 20 mM. 3. The apparent Menten-Michaelis constants for pyruvate and 2-oxoglutarate were of a 10(-4) M and for L-glutamate and L-alanine of a 10(-3) M order and were approximately the same for both fractions. 4. The ratio of the initial rate of the L-alanine + 2-oxoglutarate to the L-glutamate + pyruvate transamination reaction in the cell sap and mitochondrial fractions amounted to up to 2. 5. The apparent equilibrium constant derived from the Haldane equation was 7.01 for cell sap alanine aminotransferase and 4 for the mitochondrial enzyme. 6. Increasing pyridoxal-5'-phosphate concentrations in the incubation medium were accompanied by only non-significant stimulation of alanine aminotransferase activity in the mitochondrial and cell sap fractions. 7. A comparison of the kinetic data obtained on mitochondrial and cell sap alanine aminotransferases in vitro with the actual substrate concentrations in the transamination reaction in nervous tissue in vivo indicates that the direction of the transamination reaction in situ seems to be determined simply by compartmentation and by dynamic changes in amino- and keto- substrates in the mitochondrial and cell sap spaces.

Alanine Transaminase↗

PubMed1992

[Examination of the effect of chlorfenvinphos on the activity of aminotransferase in plasma and liver in vitro].

In vitro experiments the effect of chlorfenvinphos on aminotransferases activities in rat plasma and liver homogenate cytoplasmic fraction was studied. As amino groups donors in the transamination reactions with plasma enzymes the next eight amino acids were used: alanine, aspartic acid, cysteine, phenylalanine, leucine, lysine, valine and asparagine, and with the liver cytoplasmatic enzymes--the same above mentioned without asparagine. In all these reactions as an amino groups acceptor alfa-ketoglutaric acid was used. To the incubation mixtures were added: 1 cm3 of the plasma or liver homogenate cytoplasmic fraction; 0.05 cm3 of chlorfenvinphos solution in ethyl acetate (0.17 mg/cm3) or 0.05 cm3 ethyl acetate. Aminotransferase activity was expressed as the amount of glutamate developing during 1 h incubation. Glutamic acid was determined spectrophotometrically after chromatographic separation on filter paper. Both in rat plasma and in liver cytoplasmic fraction all used amino acids as amino groups donors in the transamination reactions were shown. In the reactions with the blood plasma enzymes the most active donors were: alanine, aspartic acid and cysteine and with the participation of liver transaminases: alanine, aspartic acid and phenylalanine. As well in plasma, as in liver the greater activity of AlAT than of AspAT was observed. In the reaction with alanine and aspartate there was formed in the case of plasma 1.51 mumol Glu/cm3 and 1.00 mumol Glu/cm3 respectively and in the case of liver -69.07 mumol Glu/g and 53.26 mumol Glu/g respectively. Results of statistical analysis revealed that small plasma and liver aminotransferases inhibition was caused by the solvent, while the insecticide under test had no influence on the efficiency of transamination.

Animals↗

PubMed1991

Glutamic acid-induced shoot differentiation in tobacco callus tissues and changes in nicotine content and in activities of aminotransferases, ornithine transcarbamylase, and arginase.

Floral bud calluses of Nicotiana tabacum L. var. Anand-2 produced multiple shoots on Murashige and Skoog's (MS) medium supplemented with 2 mg/l indole-3-acetic acid (IAA), 0.4 mg/l kinetin (Kn), and L-glutamic acid (2.5 mM). However cultures of calluses on MS medium containing only the IAA and Kn did not differentiate shoots. Specific activities of phenylalanine aminotransferase, tyrosine aminotransferase, and ornithine aminotransferase were over 7-, 5- and 5-fold higher, respectively, in the glutamic acid-treated calluses than in the nonshoot-forming ones on the day of shoot emergence. Activities of ornithine transcarbamylase and arginase decreased after the onset of the differentiation process. Implications of the enzyme activities in the differentiation process and in nicotine biogenesis are discussed.

Arginase↗

PubMedDate not supplied

[Immunochemical characteristics of hydrocortisone induced and hydrocortisone non-induced rat liver tyrosine aminotransferase isoenzymes].

Two isoenzymes of tyrosine aminotransferase (induced and noninduced by hydrocortisone were isolated from rat liver tissue and subjected to chromatographic purification. Specific antibodies with high titer were obtained after immunization of rabbits by the inducible isoenzyme. The antigenic properties of the obtained tyrosine aminotransferase isoenzymes were compared after double immunodiffusion in agar and immunoelectrophoresis. The purified induced and non-induced isoenzymes were shown to possess both similar and different antigenic determinants. The data obtained suggest that differences in antigenic properties of the tyrosine aminotransferase isoenzymes reflect those variations in their structure, which are expressed as various thermostability, sensitivity to proteolytic enzymes and substrate specificity.

Animals↗

PubMedDate not supplied

[Effect of the antibiotic D-cycloserine and its dimer on the activity of tyrosine aminotransferase in liver tissue of intact, adrenalectomized and hypophysectomized rats].

In a period of lowest day activity of tyrosine aminotransferase, within 6-8 days after bilatheral adrenalectomy, the enzyme activity was decreased by about 20% as compared with an adequate control. At the same time, within a day and seven days after hypophisectomy, in rat liver tissue the enzyme activity was increased, approximately two-fold as compared with the normal state. Within four hrs after intraperitoneal administration into intact fasting rats at a dose of 2-2.5 g per 1 kg of body weight D-cycloserine and its dimer caused an induction of tyrosine aminotransferase by 75% and 180%, respectively. Induction of the enzyme by D-cycloserine and its dimer was inhibited by actinomycin D; the phenomenon was not observed in adrenalectomized rats. Within a day after hypophisectomy D-cycloserine did not cause the induction of tyrosine aminotransferase in rat liver tissue; to the contrary, the dimer of D-cycloserine caused induction of the enzyme, comparable to the ACTH effect, in liver tissue of hypophisectomized rats.

Adrenalectomy↗

PubMed1990

[Characterization of liver tyrosine aminotransferase in rats using an immunoaffinity technic].

Antisera directed against synthetic peptides with sequences that correspond to selected regions of tyrosine aminotransferase may react with the protein without affecting its biological activity. The antiserum against the theoretical N-terminal dodecapeptide recognizes the enzyme and makes it possible to detect a blocked form of the enzyme. Another form shortened by seven aminoacids and starting with Thr 8 has been found. The isolation of tyrosine aminotransferase by one step affinity chromatography is now made possible; nevertheless the elution procedure remains a critical point. The strategy described should have further applications and allow the detailed exploration of the essential domains of aminotransferases, especially those involved in the function and the degradation of pyridoxal phosphate requiring enzymes.

Animals↗

PubMed1991

Alanine aminotransferase in clinical practice. A review.

Alanine aminotransferase is an enzyme produced mainly in the liver. When serum activity is measured, it provides a marker of hepatic disease. This review explores the biochemistry and laboratory analysis of alanine aminotransferase in terms of its significance in human health and disease. Cut-off levels that define abnormality are rather arbitrary and this decreases the specificity of the test in apparently healthy patients. A small, but important, group of patients with alanine aminotransferase abnormality have underlying liver disease that may be treatable. Most can be diagnosed based on history, physical examination, and biochemical-serological profiles. Liver biopsy can complement the diagnostic process in selected circumstances. Literature pertaining to this is critically reviewed.

Alanine Transaminase↗

PubMed1977

On the inactivation of hepatic tyrosine aminotransferase.

Tyrosine aminotransferase from frog liver requires no exogenous pyridoxal-5'-phosphate for maximum activity. The cofactor cannot be removed from the enzyme by dialysis as in the case of the rat enzyme. Pyridoxal phosphate also fails to elevate frog liver tyrosine aminotransferase activity in vivo. The enzyme activity decreases rapidly after administration of cycloheximide, which indicates that its turnover is rapid. These results strongly contradict the cofactor-dependent model of enzyme degradation. Rat and frog liver tyrosine aminotransferases are stable in neutral homogenates at 37 degrees C but are rapidly inactivated after addition of cysteine in millimolar concentrations. This effect is probably due to cystine formed during the incubation. The rates of inactivation of the different subforms of the enzyme in this system were identical. No membrane-bound system is needed for the inactivation by cystine. It is possible that the denaturation occurs by sulfide exchange. Fructose and glucose lower the enzyme activity in both rat and frog liver to an equal extent. This effect is not due to instability of the enzyme activity in both rat and frog liver to an equal extent. This effect is not due to instability of the enzyme in the presence of sugars of their metabolites. Theories on the inactivation of enzymes will be discussed in the light of the present results.

Animals↗

PubMed1978

Changes in hepatic levels of tyrosine aminotransferase messenger RNA during induction by hydrocortisone.

Messenger RNA specific for tyrosine aminotransferase was quantitated by microinjection into oocytes of Xenopus laevis. The heterologously translated enzyme was identified by specific immunoprecipitation and found to be identical with authentic aminotransferase by several criteria. The level of functional message present in rat liver increases during hydrocortisone induction, and this increase is directly proportional to the increased rate of synthesis of the enzyme. Kinetic analysis of the changes in tyrosine aminotransferase mRNA levels during induction and withdrawal indicates that the steroid does not affect the stability of the message, which has a half-life of approximately 1.2 h. Hydrocortisone, therefore, acts to increase the rate of synthesis of the specific messenger by stimulating either its transcription or processing to functional mRNA.

Animals↗

PubMed1989

Glutamate:glyoxylate aminotransferase from the seedlings of rye (Secale cereale L.).

Glutamate:glyoxylate aminotransferase from green parts of 7-day-old rye seedlings was purified almost to homogeneity. Specific activity of the purified enzyme measured with L-glutamate and glyoxylate as substrates, was 46.1 units/mg. The enzyme activity with L-alanine and 2-oxoglutarate as substrates was higher by a factor of 1.5, whereas with L-alanine and glyoxylate or L-glutamate and pyruvate it was similar to that with L-glutamate and glyoxylate. L-Aspartate, L-arginine and L-ornithine could also serve as substrate. The reaction followed the Ping-Pong Bi Bi mechanism and Km values for L-glutamate and glyoxylate were 2.6 and 0.5 mM, respectively. Pyridoxal phosphate was found to be the coenzyme of glutamate-glyoxylate aminotransferase. This coenzyme was rather tightly bound with the enzyme protein, as the attempts at its complete resolution from the apoenzyme were unsuccessful. Pyridoxal phosphate, 2-mercaptoethanol and sucrose, or bovine serum albumin stabilized the enzyme. Molecular weight of glutamate:glyoxylate aminotransferase from rye seedlings, determined by SDS-polyacrylamide gel electrophoresis, was 58,800 +/- 2,100, whereas molecular sieving on Sephacryl S-200 gel gave values of 70,800 +/- 700 or 61,400. Similar values obtained for the denatured and nondenatured enzyme seem to indicate that it is a monomeric protein.

Coenzymes↗

PubMed1989

[Activity of alanine aminotransferase in women of child-bearing age, ill with viral hepatitis].

A study is presented of 150 patients with viral hepatitis B. They are women of the child-bearing age with different severity of the disease. A dependence was established of the increase of alanine aminotransferase activity on the level of estradiol in the blood serum under normal conditions and different forms of viral hepatitis B. The estradiol and alanine aminotransferase values wer in the more severe cases, particularly, in the ovulatory and luteinic peaks of the menstrual cycle. Results of the study allow to reconsider the norm rates of alanine aminotransferase activity in women of childbearing age as adding new data to existing ideas on the mechanisms of development of hyperenzymemia in this kind of pathology.

Adolescent↗

PubMed1987

A comparison of ornithine aminotransferase from human and rat sources.

Ornithine aminotransferase was purified from human liver, rat liver and rat kidney. Sodium dodecyl sulphate polyacrylamide gel electrophoresis indicated a subunit molecular weight of 45,000 in all three cases. Estimations of the native molecular weights of ornithine aminotransferase were determined by Sephadex G-200 chromatography in the presence and absence of 0.1% (w/v) Triton X-100. Human and rat enzymes were tetrameric in the presence of detergent but the rat subunits aggregated further in its absence. Characterisation of ornithine aminotransferase from the two rat sources indicated that they were the same protein. The human and rat enzymes were similar but not identical.

Animals↗

PubMed1979

Effects of dietary vitamin B6 on the in vitro inactivation of rat tyrosine aminotransferase in host liver and Morris hepatomas.

Control rats or rats bearing Morris hepatoma 5123C (intact), 5123C (adrenalectomized), 7794A, 7800, 8999, 9121, or 9618A were fed a purified diet either deficient or adequate for vitamin B6. The concentration of pyridoxal phosphate in the plasma, host livers, and hepatomas was determined, as well as the in vitro rate of inactivation of induced tyrosine aminotransferase in homogenates of host livers and hepatomas. The results demonstrated the presence of a cysteine-independent inactivating system for tyrosine aminotransferase in hepatomas 5123C (adrenalectomized), 7800, 8999, and 9121. Only in hepatoma 9121 was there a dramatic influence of the dietary vitamin B6 on the rate of cysteine-independent inactivation. A cysteine-dependent inactivating system for the enzyme was present in all host livers and hepatomas. The rate of this in vitro inactivation for both host livers and hepatomas apparently was a function of the concentration of pyridoxal phosphate, but inactivation of tyrosine aminotransferase occurred at a significantly lower concentration of pyridoxal phosphate in the hepatomas than in the host livers.

Animals↗

PubMedDate not supplied

Effects of X-rays or aseptic inflammatory reaction on the circadian rhythm of tyrosine aminotransferase in mouse liver (TAT activity of mouse liver).

Effects of x-rays or aseptic inflammatory reaction on the circadian rhythm of tyrosine aminotransferase in mouse liver (TAT activity of mouse liver). Acta physiol. pol., 1979, 30 (4): 479--487. The circadian rhythm of tyrosine aminotransferase (TAT) was investigated during 48 hours in the liver of mice subjected to: -- subcutaneous inflammatory reaction -- ionizing radiation. The cyclic changes in the circadian enzyme activity were described with a harmonic function. In relation to the control mice in the experimental mice statistically significant changes were demonstrated in the activity of tyrosine aminotransferase associated with desynchronization of the circadian TAT rhythm, particularly evident in the first hours of the first day of the experiment. The functions of enzyme activity changed in the second 24-hour period showed, both qualitatively and quantitatively, a tendency for a gradual return of normal TAT activity in the 24-hour periods.

Animals↗