Enzymes: Properties, Mechanisms, and Factors | 酶：性质、作用机制与影响因素

📚 Enzymes: Properties, Mechanisms, and Factors | 酶：性质、作用机制与影响因素

Enzymes are biological catalysts that speed up chemical reactions in living organisms without being used up. They control everything from digestion to DNA replication, and their study is essential for understanding life at the molecular level.

酶是生物催化剂，能在生物体内加速化学反应而不被消耗。它们控制着从消化到DNA复制等一切生命活动，因此研究酶是理解生命分子基础的关键。

1. What Are Enzymes? | 什么是酶？

Enzymes are proteins made of long chains of amino acids folded into specific three-dimensional shapes. The unique shape includes an active site where substrate molecules bind.

酶是由长链条的氨基酸折叠成特定三维空间结构的蛋白质。其独特形状包含一个与底物分子结合的活性位点。

Enzymes lower the activation energy required for a reaction, allowing reactions to proceed rapidly at normal body temperatures. Without enzymes, most metabolic reactions would be far too slow to sustain life.

酶能降低反应所需的活化能，使反应在正常体温下快速进行。如果没有酶，绝大多数代谢反应将慢到无法维持生命。

Key properties of enzymes include:

酶的关键特性包括：

They are biological catalysts – they speed up reactions but remain unchanged.
它们是生物催化剂——加速反应但自身不发生改变。
They are specific – each enzyme usually acts on one substrate only.
它们具有专一性——通常只作用于一种底物。
They are affected by temperature and pH.
它们受温度和pH影响。
They can be denatured by high temperatures or extreme pH.
高温或极端pH可使它们变性失活。

2. Enzyme Specificity | 酶的专一性

Each enzyme has an active site with a distinctive shape that only fits specific substrate molecules. This is why enzymes are said to be specific – they only catalyse one reaction or a small group of reactions.

每种酶都有一个形状独特的活性位点，只能匹配特定的底物分子。因此我们说酶具有专一性——它们只催化一种或少数几种反应。

For example, sucrase only breaks down sucrose, while lipase only breaks down lipids. This specificity prevents harmful side reactions and ensures efficient control of metabolic pathways.

例如，蔗糖酶只分解蔗糖，而脂肪酶只分解脂质。这种专一性防止了有害副反应，并确保代谢途径得到高效调控。

3. Lock and Key Model | 锁钥模型

The earliest model of enzyme action compares the enzyme to a lock and the substrate to a key. Only the correct key (substrate) can fit into the lock (active site) and trigger the reaction.

最早的酶作用模型将酶比作锁，底物比作钥匙。只有正确的钥匙（底物）才能插入锁孔（活性位点）并引发反应。

This model explains enzyme specificity: if the substrate shape does not match the active site exactly, the enzyme cannot bind it and catalysis does not occur.

该模型解释了酶的专一性：如果底物形状不能精确匹配活性位点，酶便无法结合底物，催化反应也不会发生。

4. Induced Fit Model | 诱导契合模型

Modern research supports the induced fit model. In this model, the active site is flexible and changes shape slightly when the substrate binds, moulding around the substrate to strengthen the interaction.

现代研究支持诱导契合模型。在该模型中，活性位点是柔性的，底物结合时其形状会略微改变，像模具一样包住底物以加强相互作用。

The induced fit model better explains why some enzymes can catalyse reactions on substrates with slightly different structures, and it also accounts for the stabilisation of the transition state during catalysis.

诱导契合模型更好地解释了为什么一些酶可以催化结构略有不同的底物，也说明了催化过程中过渡态的稳定化机制。

Enzyme (E) + Substrate (S) ⇌ Enzyme-Substrate complex (ES) → Enzyme (E) + Product (P)

酶 (E) + 底物 (S) ⇌ 酶-底物复合物 (ES) → 酶 (E) + 产物 (P)

5. Factors Affecting Enzyme Activity | 影响酶活性的因素

The rate of an enzyme-controlled reaction depends on several factors, including temperature, pH, enzyme concentration, substrate concentration, and the presence of inhibitors.

酶促反应速率取决于多个因素，包括温度、pH、酶浓度、底物浓度以及抑制剂的存在。

Understanding these factors is important for controlling biological processes in medicine, industry, and everyday life, such as using washing powders with enzymes or optimising fermentation.

理解这些因素对在医学、工业及日常生活中控制生物过程十分重要，例如使用含酶的洗衣粉或优化发酵工艺。

6. Effect of Temperature | 温度的影响

As temperature rises from low values, the kinetic energy of molecules increases, so enzyme and substrate molecules collide more frequently, and the rate of reaction increases.

当温度从低温升高时，分子动能增加，酶和底物分子碰撞更频繁，因此反应速率加快。

However, above the optimum temperature (usually around 37°C in human cells), vibrations inside the enzyme break the weak bonds that maintain its shape. The active site changes shape, and the enzyme becomes denatured.

然而，超过最适温度（人体细胞内通常约为37°C）后，酶内部的振动会破坏维持其形状的弱键。活性位点发生改变，酶便会变性失活。

Graphs of enzyme activity against temperature show a peak at the optimum temperature, followed by a rapid drop as denaturation occurs.

酶活性随温度变化的曲线在最适温度处出现峰值，之后由于变性发生而迅速下降。

7. Effect of pH | pH的影响

Each enzyme has an optimum pH at which it works best. For most human enzymes, the optimum pH is around 7.4, close to blood pH.

每种酶都有其最适pH。大多数人体酶的最适pH约为7.4，接近血液的pH。

Exceptions include pepsin in the stomach, which works best at pH 2, and pancreatic enzymes, which work best at pH 8.5 in the small intestine.

例外包括胃中的胃蛋白酶，其最适pH为2；以及小肠中胰酶，其最适pH约为8.5。

Extreme pH values alter the charges on amino acid side chains and disrupt hydrogen bonds and ionic bonds, causing the active site to change shape and the enzyme to denature.

极端pH会改变氨基酸侧链上的电荷，破坏氢键和离子键，导致活性位点形状改变，酶变性失活。

Enzyme	Optimum pH	Location
Pepsin	2	Stomach
Salivary amylase	7	Mouth
Pancreatic lipase	8.5	Small intestine

8. Enzyme Concentration | 酶浓度

If substrate concentration is fixed and in excess, increasing the enzyme concentration increases the rate of reaction because more active sites are available to bind substrate molecules.

如果底物浓度固定且过量，增加酶浓度会加快反应速率，因为可以用更多的活性位点来结合底物分子。

With a fixed amount of substrate, enzyme concentration will eventually stop having an effect, because all substrate molecules are already occupied by enzymes.

在底物量固定时，当所有底物分子都已被酶占据，再增加酶浓度则不再影响反应速率。

9. Substrate Concentration | 底物浓度

When enzyme concentration is constant, increasing substrate concentration initially increases the rate of reaction, because more substrate molecules collide with the active sites per second.

当酶浓度恒定时，一开始增加底物浓度会提高反应速率，因为每秒有更多底物分子与活性位点碰撞。

At a high substrate concentration, the enzyme active sites become saturated; all active sites are constantly occupied, and further increases in substrate do not increase the reaction rate.

当底物浓度很高时，酶的活性位点达到饱和；所有活性位点都被持续占据，此时继续增加底物不会提高反应速率。

10. Enzyme Inhibition | 酶抑制作用

Certain substances can reduce or stop enzyme activity. Competitive inhibitors bind to the active site, blocking the substrate. Non-competitive inhibitors bind to another site, altering the enzyme’s shape.

某些物质可以降低或停止酶活性。竞争性抑制剂与活性位点结合，阻断底物；非竞争性抑制剂结合在别的位置，改变酶的形状。

In addition, heavy metals such as lead and mercury can cause denaturation by breaking disulfide bonds. Many pesticides and drugs work as enzyme inhibitors to control pests or disease.

此外，铅和汞等重金属会通过破坏二硫键导致酶变性。许多杀虫剂和药物就是通过作为酶抑制剂来控制害虫或治疗疾病。

Competitive inhibitors – compete with substrate for the active site; rate can be restored by adding more substrate.
竞争性抑制剂——与底物竞争活性位点；增加底物浓度可以恢复反应速率。
Non-competitive inhibitors – bind away from the active site; adding more substrate does not restore activity.
非竞争性抑制剂——结合在活性位点之外；增加底物无法恢复活性。

11. Uses of Enzymes | 酶的应用

Enzymes are widely used in industry and medicine. Biological washing powders contain proteases and lipases to break down protein and fat stains at lower temperatures.

酶在工业和医学中应用广泛。生物洗衣粉含有蛋白酶和脂肪酶，能在较低温度下分解蛋白质和油渍。

Other important applications include:

其他重要应用包括：

Using amylase to convert starch into sugar syrup in food production.
在食品生产中利用淀粉酶将淀粉转化为糖浆。
Using pectinase to clarify fruit juices.
利用果胶酶澄清果汁。
Using lactase to produce lactose-free milk for people with lactose intolerance.
利用乳糖酶为乳糖不耐受人群生产无乳糖牛奶。
Using enzymes in diagnostic tests and biosensors, such as glucose test strips.
在诊断测试和生物传感器（如葡萄糖试纸）中使用酶。

12. Summary | 总结

Enzymes are essential biological molecules that catalyse nearly every reaction in cells. Their specificity, efficiency, and sensitivity to environmental conditions allow organisms to regulate metabolism precisely.

酶是生命必需生物分子，几乎催化细胞内的每一个反应。它们的专一性、高效性以及对环境条件的敏感性使生物能够精准调控代谢。

In examinations, remember the lock-and-key and induced fit models, how temperature and pH cause denaturation, and how substrate and enzyme concentrations affect reaction rate. Practice drawing and interpreting graphs of enzyme activity.

在考试中，需牢记锁钥模型和诱导契合模型，理解温度和pH如何导致变性，以及底物和酶浓度如何影响反应速率。多练习绘制和解读酶活性曲线图。

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Enzymes: Properties, Mechanisms, and Factors | 酶：性质、作用机制与影响因素