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At least 973 records · Page 54Linked to original sources
PubMed1976

Simultaneous purification of mitochondrial and cytoplasmic isozymes of aspartate aminotransferase from beef kidney.

Mitochondrial and cytoplasmic isozymes of aspartate transaminase are separated from beef kidney homogenates by ammonium sulfate fractionation. The mitochondrial isozyme is purified essentially as described earlier (Eur. J. Biochem., 1972, 26, 196-206) with slight modification in order to increase the yield. The cytoplasmic isozyme is purified by heat treatment followed by ion exchange cellulose chromatography and gel chromatography. The enzyme is pure in the ultracentrifuge and in polyacrylamide gel electrophoresis; it shows only one anionic band and no subforms. It has a molecular weight of 93,000 +/- 2000 and is composed of two subunits of 46,000 M.W. The enzyme has a specific activity of 49 micronmoles of oxalacetate x min-1 x mg-1. It contains 5 SH groups per subunit; three are directly titratable with p-mercuribenzoate and the other two only after addition of 0.2% SDS; there is no evidence of S-S groups. Km values for aspartate, glutamate, alpha-ketoglutarate and oxalacetate are in the order 1.25, 3.2, 0.06 and 0.41 mM in the cytoplasmic isozyme and 0.7, 5.0, 1.25 and 0.12 mM in the mitochondrial one.

Amino Acids↗
PubMed1968

Aspartate aminotransferase. The effects of ionic concentration of kinetic constants of both isoenzymes.

1. The Michaelis constants for both isoenzymes for both substrates depend strongly on ionic concentration, being approximately proportional to phosphate concentration over considerable ranges. This is probably an effect of anions only. 2. In the absence of added salt, K(m) (2-oxoglutarate) (anionic isoenzyme) is so small as to be indeterminate. 3. K(m) (l-aspartate) (anionic isoenzyme) passes through a sharp minimum at about 3.3mm-phosphate. It is not clear whether this is a specific effect of phosphate. 4. Both substrates are inhibitory at sufficiently low ionic concentrations. 5. A modified graphical procedure is described for the derivation of the kinetic constants.

Aspartate Aminotransferases↗
PubMed1987

Substitution of an arginyl residue for the active site lysyl residue (Lys258) of aspartate aminotransferase.

The active site lysyl residue (Lys258) of E. coli aspartate amino transferase was substituted for an arginyl residue by oligonucleotide-directed, site-specific mutagenesis. The mutant enzyme was obviously unable to form an aldimine bond with pyridoxal 5'-phosphate but firmly bound the coenzyme. The finding that the mutation did not lead to entire loss in the enzymic activity suggests that Lys258 may not be essential but auxiliary for enzymic catalysis. It is also conceived that the positive charge provided by Arg258 may contribute to the enzymic catalysis.

Amino Acid Sequence↗
PubMed1983

Aspartate aminotransferase isoenzymes--differential kinetic assay in serum.

The isoenzymes of aspartate transaminase differ in their kinetic properties in that the cytoplasmic isoenzyme is more readily inhibited by adipate and by 2-oxoglutarate (substrate) at low pH. A differential kinetic assay based on this phenomenon has been optimised for use in assays of serum samples. The new method agrees well with an immune absorption procedure. Methods based on chromatographic separation of the isoenzymes fail in the presence of serum.

Adolescent↗
PubMed2001

Purification and characterization of aspartate aminotransferase from developing embryos of the camel tick Hyalomma dromedarii.

Aspartate transaminase (AST) activity in the camel tick Hyalomma dromedarii was followed throughout embryogenesis. During purification of AST to homogeneity, ion exchange chromatography lead to four separate forms (termed I, II, III and IV). AST II with the highest specific activity was pure after chromatography on Sephacryl S-300. The molecular mass of AST II was 52 KDa for the native enzyme, composed of one subunit of 50 KDa. AST II had a Km value of 0.67mM for a-ketoglutarate and 15.1 mM for aspartate. AST II had a pH optimum of 7.5 with heat stability up to 50 degrees C for 15 min. The enzyme was activated by MnCl2, and inhibited by CaCl2, MgCl2. NiCl2, and ZnCl2.

Animals↗