Prathumpai W, Gabelgaard J B, Wanchanthuek P, van de Vondervoort P J I, de Groot M J L, McIntyre M, Nielsen J
Center for Process Biotechnology, BioCentrum-DTU, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark.
Biotechnol Prog. 2003 Jul-Aug;19(4):1136-41. doi: 10.1021/bp034020r.
A kinetic model for xylose catabolism in Aspergillus is proposed. From a thermodynamic analysis it was found that the intermediate xylitol will accumulate during xylose catabolism. Use of the kinetic model allowed metabolic control analysis (MCA) of the xylose catabolic pathway to be carried out, and flux control was shown to be dependent on the metabolite levels. Due to thermodynamic constraints, flux control may reside at the first step in the pathway, i.e., at the xylose reductase, even when the intracellular xylitol concentration is high. On the basis of the kinetic analysis, the general dogma specifying that flux control often resides at the step following an intermediate present at high concentrations was, therefore, shown not to hold. The intracellular xylitol concentration was measured in batch cultivations of two different strains of Aspergillus niger and two different strains of Aspergillus nidulans grown on media containing xylose, and a concentration up to 30 mM was found. Applying MCA showed that the first polyol dehydrogenase (XDH) in the catabolic pathway of xylose exerted the main flux control in the two strains of A. nidulans and A. niger NW324, but the flux control was exerted mainly at the first enzyme of the pathway (XR) of A. niger NW 296.
提出了一种用于黑曲霉木糖分解代谢的动力学模型。通过热力学分析发现，在木糖分解代谢过程中，中间产物木糖醇会积累。利用该动力学模型可以对木糖分解代谢途径进行代谢控制分析（MCA），结果表明通量控制取决于代谢物水平。由于热力学限制，即使细胞内木糖醇浓度很高，通量控制可能仍位于该途径的第一步，即木糖还原酶处。基于动力学分析，因此表明通常认为通量控制常常位于高浓度存在的中间产物之后的步骤这一普遍观点并不成立。在以木糖为培养基培养的两种不同黑曲霉菌株和两种不同构巢曲霉菌株的分批培养中，测定了细胞内木糖醇浓度，发现其浓度高达30 mM。应用MCA表明，木糖分解代谢途径中的第一个多元醇脱氢酶（XDH）在两种构巢曲霉和黑曲霉NW324菌株中发挥主要的通量控制作用，但通量控制主要由黑曲霉NW 296菌株途径的第一个酶（XR）发挥。
