Leyval D, Uy D, Delaunay Stéphane, Goergen J L, Engasser J M
Laboratoire Bioprocédés Agro-Alimentaires, ENSAIA, Institut National Polytechnique de Lorraine-2, Avenue de la Forêt de Haye, BP 172, F-54505 Vandoeuvre-lès-Nancy cedex, France.
J Biotechnol. 2003 Sep 4;104(1-3):241-52. doi: 10.1016/s0168-1656(03)00162-7.
The enzyme activities of the valine biosynthetic pathway and their regulation have been studied in the valine-producing strain, Corynebacterium glutamicum 13032DeltailvApJC1ilvBNCD. In this micro-organism, this pathway might involve up to five enzyme activities: acetohydroxy acid synthase (AHAS), acetohydroxy acid isomeroreductase (AHAIR), dihydroxyacid dehydratase and transaminases B and C. For each enzyme, kinetic parameters (optimal temperature, optimal pH and affinity for substrates) were determined. The first enzyme of the pathway, AHAS, was shown to exhibit a weak affinity for pyruvate (K(m)=8.3 mM). It appeared that valine and leucine inhibited the three first steps of the pathway (AHAS, AHAIR and DHAD). Moreover, the AHAS activity was inhibited by isoleucine. Considering the kinetic data collected during this work, AHAS would be a key enzyme for further strain improvement intending to increase the valine production by C. glutamicum.
已对产缬氨酸菌株谷氨酸棒杆菌13032DeltailvApJC1ilvBNCD中缬氨酸生物合成途径的酶活性及其调控进行了研究。在这种微生物中，该途径可能涉及多达五种酶活性：乙酰羟酸合酶（AHAS）、乙酰羟酸异构还原酶（AHAIR）、二羟酸脱水酶以及转氨酶B和C。针对每种酶，测定了动力学参数（最适温度、最适pH值和对底物的亲和力）。该途径的第一种酶AHAS对丙酮酸表现出较弱的亲和力（K(m)=8.3 mM）。缬氨酸和亮氨酸似乎抑制该途径的前三个步骤（AHAS、AHAIR和DHAD）。此外，AHAS活性受到异亮氨酸的抑制。考虑到在这项工作中收集的动力学数据，AHAS将是进一步改良菌株以提高谷氨酸棒杆菌缬氨酸产量的关键酶。
