First cloning and characterization of aspartate aminotransferase from river buffalo (Bubalus bubalis)

Aspartate aminotransferase catalyzes the transfer of an amino group from L-aspartate to α-oxoglutarate. We have purified cytosolic isozyme, to apparent homogeneity, from the heart of river buffalo. In order to clone the enzyme total RNA was isolated and the cDNA encoding complete polypeptide of 413 amino acids was amplified by reverse transcriptase polymerase chain reaction. The cDNA and the deduced amino acid sequence exhibited 98.2% and 99.5% identities, respectively, with that of cow. The cDNA was overexpressed in Escherichia coli and the gene product was obtained in enzymologically active form. The recombinant enzyme was about 40% of the total cell proteins. The purified recombinant enzyme displayed specific activity, Km, temperature and pH stability values similar to that of the native enzyme. Edman degradation and electrospray ionization mass spectra showed that the recombinant enzyme consisted of three species having N-terminal sequences of MAPPSIF, APPSIF and PPSIF, although the second one was the predominant species. Conditions are also described, which in the mass spectral analysis give either the three species corresponding to the apo- or the holo-enzyme; the latter retaining pyridoxal phosphate bound to the protein. To our knowledge this is the first report on sequence determination, cloning and characterization of aspartate aminotransferase from river buffalo.