Vanhommerig S A, Sluyterman L A, Meijer E M
Laboratory of Organic Chemistry, Eindhoven University of Technology, The Netherlands.
Biochim Biophys Acta. 1996 Jul 18;1295(2):125-38. doi: 10.1016/0167-4838(96)00026-x.
Poly(ethylene glycol)-bound nicotinamide adenine dinucleotide (PEG-NAD+) has been successfully employed in the continuous production of L-amino acids from the corresponding alpha-keto acids by stereospecific reductive amination. Like many other dehydrogenases also horse liver alcohol dehydrogenase (HLADH) appears to be active with PEG-NAD+ as coenzyme, although the turnover number is three to four times lower. The possibilities were considered that the PEG-tail of a PEG-NAD+ bound to one active site of the HLADH dimer prevents the binding of another PEG-NAD+ to the second site, or that the PEG-tail causes destabilization of the active dimer. Both could be ruled out by kinetic studies. Neither can the observed lower intrinsic reactivity of PEG-NAD+ account for the diminished activity of the enzyme. Molecular dynamics studies, on the other hand, show that the pulling action of the polymer chain shifts the NAD position in the active site in the outside direction, causing small but significant changes in the enzyme/coenzyme interactions of a sufficient extent to explain the experimental results.
聚乙二醇结合的烟酰胺腺嘌呤二核苷酸（PEG-NAD+）已成功用于通过立体特异性还原胺化从相应的α-酮酸连续生产L-氨基酸。与许多其他脱氢酶一样，马肝醇脱氢酶（HLADH）似乎也能以PEG-NAD+作为辅酶发挥作用，尽管其周转数要低三到四倍。曾考虑过两种可能性：与HLADH二聚体一个活性位点结合的PEG-NAD+的PEG尾部会阻止另一个PEG-NAD+与第二个位点结合，或者PEG尾部会导致活性二聚体不稳定。动力学研究排除了这两种可能性。观察到的PEG-NAD+较低的内在反应活性也无法解释该酶活性的降低。另一方面，分子动力学研究表明，聚合物链的拉动作用使活性位点中的NAD位置向外移动，导致酶/辅酶相互作用发生微小但显著的变化，其程度足以解释实验结果。
