Ali Sikander, Haq Ikram Ul, Qadeer Muhammad A, Rajoka Muhammad I
Biotechnology Research Laboratory, Department of Botany, Government College, Lahore, Pakistan.
Biotechnol Appl Biochem. 2005 Oct;42(Pt 2):143-9. doi: 10.1042/BA20040180.
Aspergillus oryzae mutant strain UV-7 was further improved for the production of L-dopa from L-tyrosine using chemical mutation. Different putative mutant strains of the organism were tested for the production of L-dopa in triplicate shake-flask cultures. Among these putative mutants, the strain designated SI-12 gave a maximal production of L-dopa (444+/-14 mg of L-dopa/g of cells). The regulation of L-dopa from different carbon source solutions [initial substrate concentration (S(0))=30 g/l] by the mutant culture was investigated. At an initial pH (pH(0)) of 5.0 and a temperature (T) of 30 degrees C, 100% of sugars were utilized for product and cell mass formation, corresponding to final L-dopa product yield of 189+/-8 mg/g of substrate utilized and maximum volumetric and specific productivities of 145+/-5 mg/h per litre and 155+/-8 mg/h per g of cells respectively. There was up to 3-fold enhancement in product formation rate. This enhancement is, to our knowledge, the highest reported in the literature. To explain the kinetic mechanism of L-dopa formation and its thermal inactivation, the thermodynamic parameters were determined with the application of the Arrhenius model. Activation enthalpy and entropy for product formation, in the case of the mutant derivative, were 40 kJ/mol and 0.076 kJ.mol(-1).K(-1) for its production and 116 kJ/mol and 0.590 kJ.mol(-1).K(-1) for thermal inactivation respectively. The respective values for product formation and product de-activation were lower than the respective values for the parental culture. Therefore the mutant strain was thermodynamically more resistant to thermal denaturation during the product-formation process.
利用化学诱变对米曲霉突变株UV - 7进行进一步改良，以提高其从L - 酪氨酸生产L - 多巴的能力。在摇瓶培养中对该生物体的不同假定突变株进行了三次重复测试，以检测L - 多巴的产量。在这些假定突变株中，命名为SI - 12的菌株L - 多巴产量最高（444±14 mg L - 多巴/ g细胞）。研究了突变培养物对不同碳源溶液[初始底物浓度（S(0)）= 30 g / l]中L - 多巴的调控。在初始pH（pH(0)）为5.0、温度（T）为30℃时，100%的糖类用于产物和细胞质量的形成，相应的最终L - 多巴产物产率为189±8 mg / g利用的底物，最大体积产率和比产率分别为145±5 mg /（h·L）和155±8 mg /（h·g细胞）。产物形成速率提高了3倍。据我们所知，这种提高是文献报道中最高的。为了解释L - 多巴形成及其热失活的动力学机制，应用阿伦尼乌斯模型测定了热力学参数。突变衍生物产物形成的活化焓和熵分别为40 kJ / mol和0.076 kJ·mol⁻¹·K⁻¹，热失活的活化焓和熵分别为116 kJ / mol和0.590 kJ·mol⁻¹·K⁻¹。产物形成和产物失活的相应值低于亲本培养物的相应值。因此，突变株在产物形成过程中对热变性具有更高的热力学抗性。
