Heymann H, Günther S
Medizinische Hochschule Hannover, Zentrum Biochemie, Arbeitsbereich Enzymologie, Germany.
Biol Chem Hoppe Seyler. 1994 Jul;375(7):451-5. doi: 10.1515/bchm3.1994.375.7.451.
Several years ago, Hiromi et al. (1973) Biochim. Biophys. Acta 302, 362-375 proposed a theory for the action patterns of glucoamylases, based on data from steady-state kinetics. The Michaelis-Menten constants (Km) and the turnover number for maltooligosaccharides were used to evaluate the subsite affinities. We have now used this method for evaluating the subsite affinities for glucoamylases(EC 3.2.1.3)-maltase (EC 3.2.1.20) from human intestinal mucosa. For calculation of the subsite affinities, A1 and A2, and the intrinsic rate constant kint, we use a modified algorithm and a computer program for nonlinear least square fitting. Considerable substrate inhibition was shown by maltotriose, minor inhibition by maltotetraose, and no inhibition by maltose and the other maltooligosaccharides. This indicates a more complex kinetic behaviour of the enzyme with respect to maltotriose. Evaluation of the subsites reveals that A2 is the main binding site (18.1 kJ/mol), whereas the other affinities, with the exception of A1, are lower than 2.5 kJ/mol.
几年前，Hiromi等人（1973年，《生物化学与生物物理学报》302卷，362 - 375页）基于稳态动力学数据提出了一种关于葡糖淀粉酶作用模式的理论。米氏常数（Km）和麦芽低聚糖的转换数被用于评估亚位点亲和力。我们现在已使用这种方法来评估来自人肠黏膜的葡糖淀粉酶（EC 3.2.1.3） - 麦芽糖酶（EC 3.2.1.20）的亚位点亲和力。为了计算亚位点亲和力A1和A2以及内在速率常数kint，我们使用一种改进的算法和一个用于非线性最小二乘法拟合的计算机程序。麦芽三糖表现出相当程度的底物抑制，麦芽四糖表现出轻微抑制，而麦芽糖和其他麦芽低聚糖则无抑制作用。这表明该酶对麦芽三糖具有更复杂的动力学行为。对亚位点的评估表明，A2是主要结合位点（18.1 kJ/mol），而除A1外的其他亲和力均低于2.5 kJ/mol。
