含义Meaning
抑制剂与底物竞争同一活性部位：表观 \(K_\mathrm{M}\) 增大为 \(\alpha K_\mathrm{M}\)，\(V_{\max}\) 不变，足够高的底物浓度可以克服抑制。
The inhibitor competes with substrate for the active site: apparent \(K_\mathrm{M}\) rises to \(\alpha K_\mathrm{M}\), \(V_{\max}\) is unchanged, and enough substrate overcomes inhibition.
符号说明Symbols
| 符号Symbol | 含义 Meaning | 单位 Unit |
|---|---|---|
| \([\mathrm{I}]\) | 抑制剂浓度inhibitor concentration | mol·L⁻¹ |
| \(K_\mathrm{I}\) | 抑制常数 [E][I]/[EI]inhibition constant [E][I]/[EI] | mol·L⁻¹ |
| \(\alpha\) | 抑制因子inhibition factor | 1 |
推导Derivation
增加平衡 \(\mathrm{E} + \mathrm{I} \rightleftharpoons \mathrm{EI}\)，\(K_\mathrm{I} = [\mathrm{E}][\mathrm{I}]/[\mathrm{EI}]\)，EI 不结合底物。
Add \(\mathrm{E} + \mathrm{I} \rightleftharpoons \mathrm{EI}\) with \(K_\mathrm{I} = [\mathrm{E}][\mathrm{I}]/[\mathrm{EI}]\); EI cannot bind S.
酶守恒：\([\mathrm{E}]_0 = [\mathrm{E}] + [\mathrm{ES}] + [\mathrm{EI}] = [\mathrm{E}]\alpha + [\mathrm{ES}]\)。
Conservation: \([\mathrm{E}]_0 = [\mathrm{E}]\alpha + [\mathrm{ES}]\).
结合稳态 \([\mathrm{E}][\mathrm{S}] = K_\mathrm{M}[\mathrm{ES}]\) 解出 \([\mathrm{ES}] = [\mathrm{E}]_0[\mathrm{S}]/(\alpha K_\mathrm{M} + [\mathrm{S}])\)，乘以 \(k_\mathrm{cat}\)。
With the steady state \([\mathrm{E}][\mathrm{S}] = K_\mathrm{M}[\mathrm{ES}]\), solve for [ES] and multiply by \(k_\mathrm{cat}\).
由 \(K_\mathrm{I}\) 与 \(\mathrm{IC_{50}}\) 的关系（程–普鲁索夫）：\(K_\mathrm{I} = \mathrm{IC_{50}}/(1 + [\mathrm{S}]/K_\mathrm{M})\)。
Cheng–Prusoff: \(K_\mathrm{I} = \mathrm{IC_{50}}/(1 + [\mathrm{S}]/K_\mathrm{M})\).
适用条件与局限Assumptions & limitations
假设抑制可逆且快速平衡；不可逆（共价）抑制剂需用时间依赖的失活动力学。
Assumes rapid, reversible binding; irreversible inhibitors need time-dependent inactivation kinetics.
例题Worked example
甲醇中毒用乙醇治疗：乙醇与甲醇竞争醇脱氢酶，减少甲醛生成。
Methanol poisoning is treated with ethanol, which competes for alcohol dehydrogenase.