Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.6.1.2 (alanine aminotransferase)
26,722 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Through the use of an assay that measures cellular capacity for specific enzyme synthesis, mRNA of alanine aminotransferase (EC 2.6.1.2; L-alanine:2-oxoglutarate aminotransferase) was found to be degraded with a half-life of 12-14 hr in cultured Reuber H-35 cells; mRNA of tyrosine aminotransferase (EC 2.6.1.5; L-tyrosine:2-oxoglutarate aminotransferase) has a half-life of 2 hr in the same cells. Rates of degradation of the mRNAs are the same whether new mRNA accumulation is blocked by removal of the steroid inducer or by inhibition of mRNA synthesis (actinomycin). Cycloheximide inhibits the normally rapid turnover of tyrosine aminotransferase mRNA, but agents such as puromycin and sodium fluoride, which disrupt polysome structure, do not alter the turnover rate of the tyrosine and alanine aminotransferase mRNAs. The tyrosine and alanine aminotransferase mRNAs appear to be translated at equivalent rates. The data suggest that the degradation rate of these two mRNAs is determined by the polynucleotide structure of the mRNA molecules at or near the site for ribosome binding and initiation.
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PMID:Differential degradation of messenger RNAs in mammalian cells. 0 77

Local inflammation evoked in Swiss albino mice by subcutaneous injection of Celite resulted in a rise of liver tyrosine aminotransferase activity and plasma level of fibrinogen and seromucoid, while liver alanine aminotransferase activity and plasma level of fibrinogen and seromucoid, while liver alanine aminotransferase activity and the plasma level of albumin and total protein remained unaltered. By measuring the incorporation of [14C] leucine, stimulation of liver and plasms protein synthesis by Celite injection was demonstrated. Administration of D-galactosamine (2-5 mg/10 g body weight) inhibited the enhanced synthesis of liver proteins, and especially of trauma-induced synthesis of plasma fibrinogen and seromucoid. The inhibitory effect of galactosamine was most pronounced when the amino sugar was injected simultaneously with Celite and then protein synthesis was measured 6 h later. The results obtained support the idea that high doses of galactosamine inhibit transcription of trauma-inducible mRNA in the liver and thus block the acute-phase response.
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PMID:Inhibition of the liver and plasma protein acute-phase response in mice by D-galactosamine. 1 81

The stabilities of nine rat liver cytosol enzymes were compared at a variety of pH values. The cytosol enzymes studied were (a) those with half-lives in vivo of 3 days or longer: lactate dehydrogenase, arginase, glyceraldehyde phosphate dehydrogenase and alanine aminotransferase, (b) those with half-lives in vivo shorter than 2 days; glucokinase, dihydroorotase, serine dehydratase and tyrosine aminotransferase and (c) catalase, which has an intermediate half-life of 2.5 days for the protein protion. All the enzymes were stable in vitro at neurtal and alkaline pH values. However, at acidic pH values (pH 4): the long-lived enzymes (a) were stable; the short-lived enzymes (b) were completely inactivated with one exception; and catalase was partially inactivated. Tyrosine aminotransferase was the exception in that it is a short-lived enzyme in vivo but stable under all conditions tested in vitro. The finding that long-lived enzymes are stable in an acid milieu and short-lived enzymes are generally unstable was only observed if certain ligands (NAD+, pyridoxal 5'-phosphate, Mn2+, amino acids) were added to the invitro system. Lysosomal extracts did not accelerate the rate of inactivation of any cytosol enzyme in acidic solutions. These results indicate that if degradation of intracellular enzymes occurs in lysosomes, acid inactivation and denaturation of enzymes may be the initial event in determining the functional half-lives of the enzymes in vivo.
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PMID:Acid inactivation of short-lived rat liver enzymes. 1 3

Whereas glucocorticoids induce TAT, TRP, GPT in liver and only TAT in HTC cells, no hormonal effect on the synthesis of these enzymes was found in Zajdela hepatoma cells grown in vivo as an ascitic tumor, or in vitro as layer cultures. Although these cells remain uninducible, the hormone penetrates normally, but a strong decrease of the specific binding of cytosol and nuclear proteins with the hormone was observed. The impairment at the level of the hormone receptors could account for the non-inducibility of enzyme synthesis in ZHC cells.
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PMID:Impairment of enzyme induction by glucocorticoids in Zajdela hepatoma cells. 1 35

Most of the hybrid clones derived from a cross of Chinese hamster fibroblasts (DON) with rat hepatoma cells (Faza 967) showed preferential loss of rat chromosomes. Two of the hybrid clones retained the rat chromosomes, and both showed extinction of 4 liver-specific enzymes: aldolase B, liver alcohol dehydrogenase, and the inducible enzymes tyrosine aminotransferase and alanine aminotransferase. Subcloning of 1 of these hybrids, which contained 2 sets of hepatoma chromosomes and 1 set of hamster chromosomes, permitted the isolation of some clones which reexpressed 1 or more of the liver-specific enzymes. Liver alcohol dehydrogenase was the most frequently reexpressed enzyme and aldolase B the least. Tyrosine aminotransferase inducibility was reexpressed independently of basal activity, and the enzyme produced by the reexpressing hybrid cells was precipitated by a specific antiserum. No correlation was detected between the presence or absence of the marker chromosomes (large metacentrics) of the hamster parent and the extinction and reexpression of the hepatic enzymes. The results reported confirm and extend to interspecific hybrids the observation of the stable and independent reexpression of tissue-specific enzymes.
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PMID:Expression of differentiated functions in hepatoma cell hybrids: IX extinction and reexpression of liver-specific enzymes in rat hepatoma-Chinese hamster fibroblast hybrids. 1 64

A cross has been performed between dedifferentiated rat hepatoma cells and the differentiated cells from which they were derived. 10 hybrid clones, containing the complete chromosome sets of both parents, show extinction of 4 liver-specific enzymes: tyrosine aminotransferase (E.C. 2.6.1.5), alanine aminotransferase (E.C. 2.6.1.2), and the liver-specific isozymes of alcohol dehydrogenase (E.C. 1.1.1.1) and aldolase (E.C. 4.1.2.13). Moreover, the 4 hybrid clones examined do not produce albumin . The only function of the differentiated parent which is not extinguished in the hybrid cells is inducibility of the aminotransferases. For 3 of the hybrid clones, extinction of 3 of the 4 enzymes is incomplete, but these clones do not differ in modal chromosome number from those which show more complete extinction of the enzymes. Subcloning of several of the hybrids revealed that the phenotype of the hybrids is very stable; 4 subclones showing reexpression of intermediate levels of the enzymes are characterized. These results show that dedifferentiation of the parental cells is not due to the simple loss of some factor required for the maintenance of expression of differentiated functions, and suggest that dedifferentiation is due to the activation of some control mechanism, whose final effect is negative, and which may be a part of the epigenotype of the embryonic hepatocyte.
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PMID:Extinction of liver-specific functions in hybrids between differentiated and dedifferentiated rat hepatoma cells. 1 65

The role of coenzyme in determining intracellular contnet of pyridoxal enzymes was assessed by analyzing effects of pyridoxine deficiency on the rapidly degraded, readily dissociable tyrosine aminotransferase (EC 2.6.1.5) and the slowly degraded, nondissociable alanine aminotransferase (EC 2.6.1.2) of rat liver. Synthesis of the tyrosine enzyme was reduced, leading to a decreased amount of this enzyme, much of which was present as active apoenzyme. Synthesis of alanine aminotransferase was unchanged but much of this enzyme was present as an inactive apoenzyme which retained immunological reactivity. Degradation rates of both enzymes (t1/2 about 1.5 h, tyrosine aminotransferase; about 3 days, alanine aminotransferase) were not changed in pyridoxine deficiency. Hence, interaction with coenzyme is not a significant determinant in intracellular degradation of these aminotransferases. Coenzymes dissociation and intracellular stability probably reflect structural features of the proteins which determine both properties.
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PMID:Role of coenzyme in aminotransferase turnover. 1 9

In an earlier report from this laboratory, one of the early manifestations of hypervitaminosis A was shown to be a marked stimulation of hepatic gluconeogenesis. In the present study, effects of feeding 30,000 IU of retinyl palmitate to young rats (80-100 g), once daily, for 2 days on the incorporation of 14C-labeled precursors into glucose and glycogen by liver slices, levels of amino acids in blood and tissues, and activities of some important amino acid catabolizing enzymes in the liver were investigated. A stimulation of hepatic gluconeogenesis in hypervitaminosis A was indicated by the increased incorporation of 14C-labeled alanine and bicarbonate into glucose and glycogen by liver slices. Excessive intake of retinol caused a marked increase in the activities of hepatic alanine aminotransferase and ornithine aminotransferase and a decrease in that of tryptophan pyrrolase, without affecting those of tyrosine aminotransferase and serine dehydratase. The ratio of NADH:NAD in the livers of rats fed excess retinol was significantly increased. It is suggested that enhancement of glucoeogenesis in hypervitaminosis A is caused by a stimulation of gluconeogenic activity of the liver.
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PMID:Early effects of hypervitaminosis A on gluconeogenic activity and amino acid metabolizing enzymes of rat liver. 2 Apr 86

Primary cultures of adult rat hepatocytes were established using two different isolation procedures: a two-step collagenase perfusion and a method using ethylenediaminetetraacetate (EDTA) as the dissociating agent. Both techniques provided good yields of hepatocytes with comparable viability. The evolution of hepato-specific protein levels and several drug-metabolizing enzyme activities were followed for 8 days in cultured hepatocytes obtained by both methods. EDTA-isolated hepatocytes maintained a low gamma glutamyltransferase (GGT) activity, whereas collagenase-treated cells acquired a high GGT level. Transferrin secretion and tyrosine aminotransferase (TAT), alanine aminotransferase (ALT), and microsomal epoxide hydrolase (mEH) activities were stable in both EDTA- and collagenase-isolated hepatocytes, whereas albumin secretion, aspartate amino transferase (AST) activity, total cytochromes P-450 content, IA1 and IIB1 P-450 isoenzymes, NADPH-cytochrome P-450 reductase (EC 1.6.2.4) levels, and bilirubin glucuronidation decreased faster in collagenase-treated cells. The most important difference observed was the maintainance of the mixed-function oxidase system in EDTA-isolated hepatocytes. These results emphasize the critical role of isolation technique in stabilization of differentiated hepatocytes in primary culture.
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PMID:Influence of the isolation method on the stability of differentiated phenotype in cultured rat hepatocytes. 185 20

The complete amino acid sequence of rat liver cytosolic alanine aminotransferase (EC 2.6.1.2) is presented. Two primary sets of overlapping fragments were obtained by cleavage of the pyridylethylated protein at methionyl and lysyl bonds with cyanogen bromide and Achromobacter protease I, respectively. The protein was found to be acetylated at the amino terminus and contained 495 amino acid residues. The molecular weight of the subunit was calculated to be 55,018 which was in good agreement with a molecular weight of 55,000 determined by SDS-PAGE and also indicated that the active enzyme with a molecular weight of 114,000 was a homodimer composed of two identical subunits. No highly homologous sequence was found in protein sequence databases except for a 20-residue sequence around the pyridoxal 5'-phosphate binding site of the pig heart enzyme [Tanase, S., Kojima, H., & Morino, Y. (1979) Biochemistry 18, 3002-3007], which was almost identical with that of residues 303-322 of the rat liver enzyme. In spite of rather low homology scores, rat alanine aminotransferase is clearly homologous to those of other aminotransferases from the same species, e.g., cytosolic tyrosine aminotransferase (24.7% identity), cytosolic aspartate aminotransferase (17.0%), and mitochondrial aspartate aminotransferase (16.0%). Most of the crucial amino acid residues hydrogen-bonding to pyridoxal 5'-phosphate identified in aspartate aminotransferase by X-ray crystallography are conserved in alanine aminotransferase. This suggests that the topology of secondary structures characteristic in the large domain of other alpha-aminotransferases with known tertiary structure may also be conserved in alanine aminotransferase.
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PMID:Complete amino acid sequence of rat liver cytosolic alanine aminotransferase. 204 42


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