King's College London, School of Medicine, Diabetes and Nutritional Sciences Division, London, UK.
Carbohydr Res. 2012 Sep 1;358:67-71. doi: 10.1016/j.carres.2012.07.004. Epub 2012 Jul 16.
For a two phase system comprising an enzyme in solution acting on an insoluble substrate such as starch, adsorption of the enzyme is a key initial step in the reaction but few studies of agents affecting direct binding have been performed. The effect of maltose on the interaction of maize starch with porcine pancreatic α-amylase was studied by using a method in which the direct binding of starch to amylase is measured under conditions of negligible catalytic activity. The dissociation constant for starch binding increased with maltose concentration and analysis of the binding showed that the kinetic action of maltose was entirely competitive. This result accords with results described in the literature in which maltose was shown to be a competitive inhibitor of amylase action. If the maltose concentration is sufficiently high, a second molecule may bind at the active site but the affinity of the second binding step is approximately 6.5-fold weaker. Because of the relatively low affinity for maltose, it seems unlikely that inhibition by maltose of the initial stage of starch-amylase interaction normally plays any role in regulating intestinal digestion of starch.
对于包含在溶液中作用于不溶性底物（如淀粉）的酶的两相体系，酶的吸附是反应的关键初始步骤，但很少有研究报道影响直接结合的试剂。本研究采用一种方法，在该方法中，在催化活性可忽略不计的条件下测量淀粉与猪胰腺α-淀粉酶之间的直接结合，研究了麦芽糖对玉米淀粉与猪胰腺α-淀粉酶相互作用的影响。淀粉结合的离解常数随麦芽糖浓度的增加而增加，结合分析表明麦芽糖的动力学作用完全是竞争性的。该结果与文献中描述的结果一致，其中麦芽糖被证明是淀粉酶作用的竞争性抑制剂。如果麦芽糖浓度足够高，则第二个分子可能在活性部位结合，但第二个结合步骤的亲和力大约弱 6.5 倍。由于对麦芽糖的亲和力相对较低，因此麦芽糖抑制淀粉-淀粉酶相互作用的初始阶段通常在调节肠道淀粉消化中发挥任何作用的可能性似乎不大。
