Brandt R B, Laux J E, Yates S W
Biochem Med Metab Biol. 1987 Jun;37(3):344-9. doi: 10.1016/0885-4505(87)90046-6.
The use of I50 (concentration of inhibitor required for 50% inhibition) for enzyme or drug studies has the disadvantage of not allowing easy comparison among data from different laboratories or under different substrate conditions. Modifications of the Michaelis-Menten equation for treatment of inhibitors can allow both the determination of the type of inhibition (competitive, noncompetitive, and uncompetitive) and the Ki for the inhibitor. For competitive and uncompetitive inhibitors when the assay conditions are [S] = Km, then Ki = I50/2. For different conditions of [S] there is a divergence between competitive and uncompetitive inhibitors that may be used to identify the type of inhibitor. The equation for Ki also differs. For noncompetitive inhibitors the Ki = I50 and this relationship is valid with changing [S]. The equations developed require a single substrate, reversible-type inhibitors, and kinetics of the Michaelis-Menten type. Examples of the use of the equations are illustrated with experimental data from scientific publications.
在酶或药物研究中使用I50（产生50%抑制作用所需的抑制剂浓度）存在一个缺点，即无法轻松比较来自不同实验室或不同底物条件下的数据。对米氏方程进行修改以处理抑制剂，既可以确定抑制类型（竞争性、非竞争性和反竞争性），也可以确定抑制剂的Ki值。对于竞争性和反竞争性抑制剂，当测定条件为[S]=Km时，那么Ki = I50/2。对于不同的[S]条件，竞争性和反竞争性抑制剂之间存在差异，可用于识别抑制剂类型。Ki的方程也不同。对于非竞争性抑制剂，Ki = I50，并且这种关系在[S]变化时仍然有效。所推导的方程需要单一底物、可逆型抑制剂以及米氏动力学类型。通过科学出版物中的实验数据说明了这些方程的使用示例。
