scholarly journals Stabilization of rat liver tyrosine aminotransferase by tetracycline

1975 ◽  
Vol 150 (3) ◽  
pp. 329-333 ◽  
Author(s):  
R Hannah ◽  
M K Sahib
Keyword(s):  
Rat Liver ◽  
De Novo ◽  
Rabbit Antiserum ◽  
Tyrosine Aminotransferase ◽  
Enzyme Inactivation ◽  
Aminotransferase Activity ◽  
Rapid Inactivation ◽  
Liver Homogenates

Rat liver tyrosine aminotransferase was purified 200-fold and an antiserum raised against it in rabbits. 2. Hepatic tyrosine aminotransferase activity was increased fourfold by tyrosine, twofold by tetracycline, 2.5-fold by cortisone 21-acetate and ninefold by a combination of tyrosine and cortisol administered intraperitoneally to rats. 3. Radioimmunoassay with 14C-labelled tyrosine aminotransferase, in conjunction with rabbit antiserum against the enzyme, revealed that cortisol stimulates the synthesis of the enzyme de novo, but that tetracycline has no such effect. 4. Incubation of rat liver homogenates with purified tyrosine aminotransferase in vitro leads to a rapid inactivation of the enzyme, which tetracycline partially inhibits. 5. The inactivation is brought about by intact lysosomes, and the addition of 10mM-cysteine increases the rate of enzyme inactivation, which is further markedly increased by 10mM-Mg2+ and 10mM-ATP. Here again tetracycline partially inhibits the decay rate, leading to the inference that the increase of tyrosine aminotransferase activity in vivo by tetracycline is brought about by the latter inhibiting the lysosomal catheptic action.

scholarly journals The effects of salicylate on the activity of rat liver tyrosine–2-oxoglutarate aminotransferase in vitro and in vivo

1972 ◽  
Vol 126 (2) ◽  
pp. 347-350 ◽  
Author(s):  
A. A.-B. Badawy
Keyword(s):  
Rat Liver ◽  
Pyridoxal Phosphate ◽  
Actinomycin D ◽  
Sodium Salicylate ◽  
Intraperitoneal Administration ◽  
Tyrosine Aminotransferase ◽  
Major Effect ◽  
Endogenous Activity

1. Salicylate, in concentrations of 0.25mm and above, enhances the basal activity of tyrosine–2-oxoglutarate aminotransferase in homogenates of rat liver incubated in the absence of added pyridoxal 5′-phosphate (endogenous activity). The effect is decreased by increasing the concentration of the cofactor. 2. The intraperitoneal administration of sodium salicylate enhances the activity of rat liver tyrosine aminotransferase; the major effect during the first hour being on the enzyme in the absence of added pyridoxal phosphate. Actinomycin D prevents the induction of the enzyme by cortisol and tryptophan. Induction by pyridoxine or salicylate is 50% inhibited by actinomycin D. The effects of the injections of various combinations of cortisol, pyridoxine and salicylate were also studied in the absence or presence of actinomycin D. 3. It is suggested that salicylate induces rat liver tyrosine aminotransferase by displacing its protein-bound cofactor and that a cofactor-type induction of the hepatic enzyme occurs in pyridoxine-treated rats.

O n the Mechanism of Inactivation and ATP-Dependent Reactivation of Rat Liver Tyrosine Aminotransferase

1977 ◽  
Vol 32 (9-10) ◽  
pp. 777-780 ◽  
Author(s):  
Hans-Heinrich Hamm ◽  
Werner Seubert
Keyword(s):  
Rat Liver ◽  
Tyrosine Aminotransferase ◽  
Particulate Fraction ◽  
Kidney Cortex ◽  
Aminotransferase Activity ◽  
Liver And Kidney ◽  
Membrane Bound ◽  
Nucleotide Specificity

Abstract The mechanism of in vitro inactivation and ATP-dependent rapid reactivation of rat liver tyrosine aminotransferase by a membrane-bound system from rat liver and kidney cortex and the nucleotide specificity of this process was investigated using partially purified tyrosine amino­ transferase as a substrate. Adenosine 5′-triphosphate (ATP) could be replaced by guanosine 5′-tri-phosphate (GTP), whereas inosine 5′-triphosphate (ITP) was less effective. During reactivation [γ-32P]A T P was incorporated into the enzyme and not excorporated by incubation of the labeled enzyme with excess non-radioative ATP. Inactivation of labeled tyrosine aminotransferase by a particulate fraction led to a decrease protein-bound radioactivity concomitant with an increase of [32P] orthophosphate. This points to a phosphorylation and dephosphorylation mechanism in the regulation of tyrosine aminotransferase activity.

scholarly journals Participation of cysteine and cystine in inactivation of tyrosine aminotransferase in rat liver homogenates

1978 ◽  
Vol 176 (2) ◽  
pp. 449-454 ◽  
Author(s):  
W T Buckley ◽  
L P Milligan
Keyword(s):  
Rat Liver ◽  
Tyrosine Aminotransferase ◽  
Particulate Fraction ◽  
Effective Agent ◽  
N2 Atmosphere ◽  
Rapid Inactivation ◽  
Lag Period ◽  
Liver Homogenates

1. Inactivation of tyrosine aminotransferase was studied in rat liver homogenates. Under an O2 atmosphere with cysteine added, inactivation was rapid after a lag period of approx. 1h, whereas a N2 atmosphere extended the lag period to approx. 3h. 2. Replacement of cysteine with cystine resulted in rapid inactivation both aerobically and anaerobically. 3. Removal of the particulate fraction by centrifuging rat liver homogenates at 13,000g for 9min resulted in an aerobic lag period of 0.5h in the presence of cystine and approx. 3h in the presence of cysteine. 4. It is proposed that the stimulatory effect of cysteine on tyrosine aminotransferase inactivation occurs largely as a result of oxidation to cystine, which appears to be a more directly effective agent.

scholarly journals Rat liver tyrosine aminotransferase activity and induction by dexamethasone upon cadmium intoxication

2003 ◽  
Vol 55 (1-2) ◽  
pp. 3-7 ◽  
Author(s):  
Jadranka Dundjerski ◽  
Jelena Predic ◽  
Aleksandra Cvoro ◽  
Gordana Matic
Keyword(s):  
Enzyme Activity ◽  
Gene Transcription ◽  
Rat Liver ◽  
Tyrosine Aminotransferase ◽  
Aminotransferase Activity ◽  
Liver Cytosol ◽  
Cadmium Intoxication ◽  
Rat Liver Cytosol

This study was focused on Cd effects on basal and dexamethasone-induced tyrosine aminotransferase (TAT) activity in the rat liver cytosol. Cadmium (Cd), applied in the dose of 2 mg/kg b.w., stimulated both TAT activity and its induction by dexamethasone, inducing the most prominent alterations 24 h after administration. Doses lower than 2 mg Cd/kg b.w. were ineffective while the higher ones (3 and 4 mg Cd/kg b.w) led to the changes similar to those reached by 2 mg Cd/kg. The in vitro application of different Cd concentrations to the liver cytosol rendered the enzyme activity unchanged suggesting that the metal acted at the level of TAT gene transcription.

scholarly journals The relative stability of liver cytosol enzymes incubated in vitro

1974 ◽  
Vol 144 (2) ◽  
pp. 371-376 ◽  
Author(s):  
M F Hopgood ◽  
F J Ballard
Keyword(s):  
Rate Constants ◽  
Phosphoenolpyruvate Carboxykinase ◽  
Tyrosine Aminotransferase ◽  
Enzyme Inactivation ◽  
Fructose Bisphosphate ◽  
Cytosol Fraction ◽  
Reverse Pattern ◽  
Glucose 6 Phosphate Dehydrogenase

1. Relative rates of enzyme inactivation were measured in liver slices, homogenates and cytosol fractions as well as in the presence of trypsin and at acid pH. The enzymes chosen are all present in the cytosol fraction of rat liver, and have widely different degradation rate constants in vivo. 2. The inactivation rates of lactate dehydrogenase, fructose bisphosphate aldolase, glucose 6-phosphate dehydrogenase, glucokinase, phosphoenolpyruvate carboxykinase (GTP), l-serine dehydratase and thymidine kinase in liver preparations at neutral pH are in a similar order to the rate constants of degradation of these enzymes in the intact animal. 3. The two exceptions of this general correlation were tyrosine aminotransferase, which was stable in vitro but not in vivo, and glyceraldehyde phosphate dehydrogenase, which shows the reverse pattern. 4. These findings generally support the concept that the same factors are responsible for enzyme inactivation in vitro as occur in the intact tissue.

scholarly journals Glutathione transferase Zeta catalyses the oxygenation of the carcinogen dichloroacetic acid to glyoxylic acid

1998 ◽  
Vol 331 (2) ◽  
pp. 371-374 ◽  
Author(s):  
Zeen TONG ◽  
Philip G. BOARD ◽  
M. W. ANDERS
Keyword(s):  
Liver Enzyme ◽  
Rat Liver ◽  
Glutathione Transferase ◽  
Gel Filtration ◽  
Rabbit Antiserum ◽  
Glyoxylic Acid ◽  
Dichloroacetic Acid ◽  
Amino Acid Residues

Dichloroacetic acid (DCA), a common drinking-water contaminant, is hepatocarcinogenic in rats and mice, and is a therapeutic agent used clinically in the management of lactic acidosis. DCA is biotransformed to glyoxylic acid by glutathione-dependent cytosolic enzymes in vitro and is metabolized to glyoxylic acid in vivo. The enzymes that catalyse the oxygenation of DCA to glyoxylic acid have not, however, been identified or characterized. In the present investigation, an enzyme that catalyses the glutathione-dependent oxygenation of DCA was purified to homogeneity (587-fold) from rat liver cytosol. SDS/PAGE and HPLC gel-filtration chromatography showed that the purified enzyme had a molecular mass of 27–28 kDa. Sequence analysis showed that the N-terminus of the purified protein was blocked. An internal sequence of 30 amino acid residues was obtained that matched the recently discovered human glutathione transferase Zeta well [Board, Baker, Chelvanayagam and Jermiin (1997) Biochem. J. 328, 929–935]. Western-blot analysis showed that the purified rat-liver enzyme cross-reacted with rabbit antiserum raised against recombinant human glutathione transferase Zeta. The apparent Km and Vmax values of the purified enzyme with DCA as the variable substrate were 71.4 µM and 1334 nmol/min per mg of protein, respectively; the Km for glutathione was 59 µM. Both the purified rat-liver enzyme and the recombinant human enzyme showed high activity with DCA as the substrate. These results demonstrate that the glutathione-dependent oxygenation of DCA to glyoxylic acid is catalysed by a Zeta-class glutathione transferase.

scholarly journals Comparison of ornithine decarboxylase from rat liver, rat hepatoma and mouse kidney

1985 ◽  
Vol 226 (2) ◽  
pp. 577-586 ◽  
Author(s):  
J E Seely ◽  
L Persson ◽  
G J Sertich ◽  
A E Pegg
Keyword(s):  
Ornithine Decarboxylase ◽  
Rat Liver ◽  
Isoelectric Point ◽  
Rabbit Antiserum ◽  
Point Interaction ◽  
Mouse Kidney ◽  
Two Dimensional Gel Electrophoresis ◽  
Morris Hepatoma

Comparisons were made of ornithine decarboxylase isolated from Morris hepatoma 7777, thioacetamide-treated rat liver and androgen-stimulated mouse kidney. The enzymes from each source were purified in parallel and their size, isoelectric point, interaction with a monoclonal antibody or a monospecific rabbit antiserum to ornithine decarboxylase, and rates of inactivation in vitro, were studied. Mouse kidney, which is a particularly rich source of ornithine decarboxylase after androgen induction, contained two distinct forms of the enzyme which differed slightly in isoelectric point, but not in Mr. Both forms had a rapid rate of turnover, and virtually all immunoreactive ornithine decarboxylase protein was lost within 4h after protein synthesis was inhibited. Only one form of ornithine decarboxylase was found in thioacetamide-treated rat liver and Morris hepatoma 7777. No differences between the rat liver and hepatoma ornithine decarboxylase protein were found, but the rat ornithine decarboxylase could be separated from the mouse kidney ornithine decarboxylase by two-dimensional gel electrophoresis. The rat protein was slightly smaller and had a slightly more acid isoelectric point. Studies of the inactivation of ornithine decarboxylase in vitro in a microsomal system [Zuretti & Gravela (1983) Biochim. Biophys. Acta 742, 269-277] showed that the enzymes from rat liver and hepatoma 7777 and mouse kidney were inactivated at the same rate. This inactivation was not due to degradation of the enzyme protein, but was probably related to the formation of inactive forms owing to the absence of thiol-reducing agents. Treatment with 1,3-diaminopropane, which is known to cause an increase in the rate of degradation of ornithine decarboxylase in vivo [Seely & Pegg (1983) Biochem. J. 216, 701-717] did not stimulate inactivation by microsomal extracts, indicating that this system does not correspond to the rate-limiting step of enzyme breakdown in vivo.

Effects of Choline Deficiency and Carnitine on Palmitic Acid Oxidation by Rat Liver Homogenates

1957 ◽  
Vol 190 (3) ◽  
pp. 449-452 ◽  
Author(s):  
Irving B. Fritz
Keyword(s):  
Palmitic Acid ◽  
Rat Liver ◽  
Fat Metabolism ◽  
Acid Oxidation ◽  
Choline Deficiency ◽  
Normal Range ◽  
Hepatic Fat ◽  
Liver Homogenates

The conversion of C14 carboxyl-labeled palmitic acid to CO2 and ketones by liver homogenates prepared from choline deficient rats maintained on a 20% protein diet was within the normal range, indicating that hepatic fat oxidation is not impaired in the absence of choline alone. Carnitine addition in vitro augmented ketogenesis by livers from all groups of rats tested, while choline addition in vitro was without effect. Choline administration in vivo resulted in an enhanced oxidation of palmitic acid to CO2 by liver homogenates obtained from choline-deficient animals. However, liver preparations from animals injected in vivo with choline continued to respond to carnitine addition in vitro with an enhanced ketogenesis. It was concluded that carnitine and choline influence different parameters of fat metabolism.

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