Aspartate aminotransferase catalyzes the transfer of an amino group from l-aspartate to α-oxoglutarate. A gene encoding aspartate aminotransferase, AST_Gt, from Geobacillus thermopakistaniensis was cloned and expressed in Escherichia coli. The purified recombinant AST_Gt exhibited highest activity at 65 °C and pH 7.0. The activity was dependent on pyridoxal phosphate but not on any metal ions. Stoichiometry of purified AST_Gt demonstrated that 0.1 pyridoxal phosphate was attached per subunit of the enzyme. Determination of molecular weight by gel filtration chromatography indicated that AST_Gt existed in a dimeric form in solution. Thermostability experiments showed no significant change in activity even after 16 h incubation at 65 °C. AST_Gt exhibited apparent V_max and K_m values of 120 μmol min⁻¹ mg⁻¹ and 1.5 mM, respectively, against l-aspartate. Substrate specificity experiments indicated the highest relative activity against aspartate (100%) followed by tyrosine (27%) and proline (16%). To the best of our knowledge, this is the first report on cloning and characterization of an AST from genus Geobacillus.

天冬氨酸氨基转移酶催化氨基从1-天冬氨酸向α-氧代戊二酸酯的转移。甲基因编码天冬氨酸转氨酶，AST_亿吨，从土芽孢thermopakistaniensis被克隆并表达在大肠杆菌中。纯化的重组AST _Gt在65°C和pH 7.0下表现出最高的活性。活性取决于磷酸吡ido醛，而不取决于任何金属离子。纯化的AST _Gt的化学计量表明，该酶的每个亚基均附着有0.1吡ido醛磷酸酯。通过凝胶过滤色谱法测定分子量表明AST _Gt在溶液中以二聚体形式存在。热稳定性实验表明，即使在65°C孵育16小时后，活性也没有明显变化。AST _Gt相对于1-天门冬_氨酸的表观V _max和K _m值分别为120μmolmin ^-1 mg ^-1和1.5 mM 。底物特异性实验表明，对天冬氨酸的相对活性最高（100％），其次是酪氨酸（27％）和脯氨酸（16％）。据我们所知，这是关于从地芽孢杆菌属中克隆和鉴定AST的第一份报告。