Enzyme Inhibitors and Their Action | 酶抑制剂及其作用

📚 Enzyme Inhibitors and Their Action | 酶抑制剂及其作用

Enzyme inhibitors are molecules that interfere with the action of an enzyme, either by slowing the reaction or stopping it altogether. They do not necessarily destroy the enzyme, and in many cases their effect is reversible.

酶抑制剂是能与酶结合并降低或阻断其催化活性的分子。它们并不一定破坏酶，很多时候其作用是可逆的。

Inhibitors can be classified in two main ways: by whether they are reversible or irreversible, and by whether they compete with the substrate for the active site.

抑制剂可按两种方式分类：根据作用是否可逆，分为可逆抑制剂和不可逆抑制剂；根据是否与底物竞争活性位点，分为竞争性抑制剂和非竞争性抑制剂。

1. What Are Enzyme Inhibitors? | 什么是酶抑制剂？

Enzyme inhibitors are essential tools in biochemistry, medicine and research. A proper understanding of them is a core requirement of the CIE A-Level biology syllabus.

酶抑制剂是生物化学、医学和研究中的重要工具，对它们的深入理解是 CIE A-Level 生物学考纲的核心要求。

• Reversible inhibitors bind loosely through non-covalent bonds and can be removed by changing conditions.

  可逆抑制剂通过非共价键松散结合，可通过改变条件而解离。

• Irreversible inhibitors form strong covalent bonds with the enzyme and permanently inactivate it.

  不可逆抑制剂与酶形成强共价键，使酶永久失活。

2. Competitive Inhibition | 竞争性抑制

In competitive inhibition, the inhibitor resembles the substrate in shape and charge, so it can bind to the active site. This prevents the real substrate from binding. The inhibitor competes with the substrate for the same site.

竞争性抑制中，抑制剂在形状和电荷上与底物相似，因此能结合活性位点，阻止真正的底物进入。抑制剂与底物竞争同一个结合位点。

E + S ⇌ ES → E + P

E + I ⇌ EI

The extent of inhibition depends on the concentrations of both substrate and inhibitor. If the substrate concentration is raised sufficiently, the enzyme will be saturated with substrate and the inhibition can be overcome.

抑制程度取决于底物和抑制剂的浓度。如果底物浓度足够高，酶将与底物达到饱和，抑制效果可被解除。

In kinetic terms, the apparent Kₘ increases, meaning a higher substrate concentration is needed to occupy half of the enzyme molecules. Vₘₐₓ remains unchanged because sufficiently high substrate can out-compete the inhibitor.

在动力学上，表观 Kₘ 增大，意味着需要更高的底物浓度才能使一半酶分子被占据。Vₘₐₓ 保持不变，因为足够高的底物浓度可以胜过抑制剂。

3. Non-Competitive Inhibition | 非竞争性抑制

A non-competitive inhibitor binds to a site other than the active site, usually an allosteric site. This binding changes the shape of the enzyme, including the active site, so that the enzyme-substrate complex cannot form effectively, or the catalytic step is slowed.

非竞争性抑制剂的结合位点在活性位点之外，通常是别构位点。这种结合改变酶的形状，包括活性位点的形状，使得酶-底物复合物不能有效形成，或催化步骤被减慢。

E + I ⇌ EI

ES + I ⇌ ESI

Unlike competitive inhibition, increasing substrate concentration cannot overcome non-competitive inhibition, because the inhibitor does not compete for the active site.

与竞争性抑制不同，增加底物浓度无法解除非竞争性抑制，因为抑制剂并不争夺活性位点。

Kinetic consequence: Vₘₐₓ is reduced because the number of functional enzyme molecules is effectively lowered. Kₘ is unchanged because the enzyme that still works has the same affinity for the substrate.

动力学结果：Vₘₐₓ 降低，因为可用酶分子的数目实际上减少；Kₘ 不变，因为仍能工作的酶对底物的亲和力没有改变。

4. Reversible and Irreversible Inhibition | 可逆抑制与不可逆抑制

Reversible inhibitors bind to enzymes non-c

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