Enzymes: Structure, Function and Applications | 酶：结构、功能与应用

📚 Enzymes: Structure, Function and Applications | 酶：结构、功能与应用

Enzymes are biological catalysts that speed up chemical reactions in living organisms by lowering the activation energy required for the reaction. They remain unchanged after the reaction and can be reused. Nearly every metabolic process in a cell requires specific enzymes.

酶是生物催化剂，通过降低反应所需的活化能来加快生物体内的化学反应。反应结束后酶本身不发生改变，因此可以重复使用。细胞中几乎每一个代谢过程都需要特定的酶。

1. What Are Enzymes? | 什么是酶？

Enzymes are usually globular proteins made of long chains of amino acids folded into a specific three-dimensional shape. Each enzyme has a region called the active site, where the substrate binds.

酶通常是球状蛋白质，由长链氨基酸折叠成特定的三维形状。每个酶都有一个称为活性位点的区域，底物在此结合。

Key characteristics of enzymes:

酶的关键特征：

They are specific to their substrates – each enzyme catalyses only one type of reaction.

它们对底物具有专一性——每种酶只催化一种类型的反应。
They are not consumed by the reaction.

它们在反应中不会被消耗。
They work best at an optimum temperature and pH.

它们在最适温度和 pH 下活性最高。
Their activity is affected by inhibitors.

它们的活性会受到抑制剂的影响。

2. The Active Site and Specificity | 活性位点与专一性

The active site is a small depression or groove in the enzyme molecule. Its shape is complementary to the substrate molecule, allowing them to bind temporarily and form an enzyme-substrate complex.

活性位点是酶分子上的一个小凹陷或沟槽。它的形状与底物分子互补，使二者能够暂时结合并形成酶-底物复合物。

Because the active site has a specific shape, only the correct substrate can fit. This explains why enzymes show absolute or relative specificity.

由于活性位点具有特定的形状，只有正确的底物才能契合。这解释了酶为何表现出绝对或相对专一性。

3. The Lock-and-Key Model | 锁钥模型

The classic model used to describe enzyme specificity is the lock-and-key model. The enzyme is the lock and the substrate is the key. Only the correct key can fit into the lock to open it, meaning only the correct substrate can bind to the active site.

描述酶专一性的经典模型是锁钥模型。酶相当于锁，底物相当于钥匙。只有正确的钥匙才能插入锁并打开它，也就是说只有正确的底物才能结合到活性位点上。

Enzyme + Substrate → Enzyme-Substrate Complex → Enzyme + Product

酶 + 底物 → 酶-底物复合物 → 酶 + 产物

Although this model is simple, it is useful for explaining how competitive inhibitors work. Later, the induced-fit model was proposed, suggesting the active site is not rigid but changes shape slightly to fit the substrate more tightly.

尽管该模型简单，但它有助于解释竞争性抑制剂的作用机制。后来人们提出了诱导契合模型，认为活性位点并非刚性，而是会稍微改变形状以更紧密地贴合底物。

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

Enzyme activity is influenced by several factors: temperature, pH, enzyme concentration, substrate concentration and the presence of inhibitors. Changing any of these can increase or decrease the rate of reaction.

酶的活性受多种因素影响：温度、pH、酶浓度、底物浓度以及有无抑制剂。改变其中任何一个因素都可能加快或减慢反应速率。

Below is a summary table:

下面是一个汇总表：

Factor \| 因素	Effect on Reaction Rate \| 对反应速率的影响
Temperature \| 温度	As temperature rises, particles gain kinetic energy; rate increases up to optimum, then decreases as enzyme is denatured. \| 温度升高，粒子获得动能，速率上升至最适点；之后酶变性，速率下降。
pH \| pH	Each enzyme has an optimum pH; too high or too low alters the active site shape and denatures the enzyme. \| 每种酶都有最适 pH；过高或过低都会改变活性位点形状并使酶变性。
Enzyme concentration \| 酶浓度	Rate increases linearly until substrate becomes limiting. \| 反应速率随酶浓度线性增加，直到底物成为限制因素。
Substrate concentration \| 底物浓度	Rate increases until all active sites are occupied; further increases do not change the rate. \| 速率上升直到所有活性位点被占据；继续增加底物浓度速率不再改变。

5. Effect of pH | pH 的影响

Every enzyme has an optimum pH at which its activity is maximum. For example, pepsin in the stomach works best at pH 2, while trypsin in the small intestine works best at pH 8.

每种酶都有其活性最大的最适 pH。例如，胃中的胃蛋白酶在 pH 2 时活性最高，而小肠中的胰蛋白酶在 pH 8 时活性最高。

When the pH moves away from the optimum, the ionic bonds and hydrogen bonds that hold the enzyme’s three-dimensional shape become disturbed. The active site changes shape, so the substrate can no longer bind. At extreme pH values, the enzyme is permanently denatured.

当 pH 偏离最适值时，维持酶三维形状的离子键和氢键受到干扰。活性位点形状改变，底物无法再结合。在极端 pH 值下，酶会发生永久性变性。

Typical graph description: A bell-shaped curve with a peak at the optimum pH.

典型曲线描述：一条钟形曲线，峰值为最适 pH。

6. Effect of Temperature | 温度的影响

At low temperatures, enzymes have low activity because molecules move slowly and fewer collisions occur. As temperature increases, the rate of reaction increases because both enzyme and substrate molecules gain kinetic energy, making more successful collisions per second.

在低温下，酶的活性较低，因为分子运动缓慢，碰撞次数少。随着温度升高，反应速率加快，因为酶和底物分子获得动能，每秒成功碰撞次数增加。

Each enzyme has an optimum temperature – for human enzymes, usually around 37°C. Above this temperature, molecular vibrations become violent and break the bonds that maintain the enzyme’s structure. The active site loses its shape and the enzyme is said to be denatured.

每种酶都有最适温度——人类酶通常在 37°C 左右。超过这一温度，分子振动变得剧烈，破坏维持酶结构的化学键。活性位点失去形状，即可说酶发生了变性。

Denaturation is permanent. The rate of reaction falls to zero once all enzyme molecules have been denatured.

变性是不可逆的。一旦所有酶分子变性，反应速率就会降为零。

7. Enzyme Concentration and Substrate Concentration | 酶浓度与底物浓度

If substrate concentration is kept constant, increasing enzyme concentration increases the rate of reaction. This is because there are more active sites available in the same volume, so more enzyme-substrate complexes can form per unit time.

如果底物浓度保持不变，增加酶浓度会使反应速率增加。这是因为单位体积内有更多可用活性位点，单位时间内能形成更多酶-底物复合物。

If enzyme concentration is kept constant, increasing substrate concentration initially increases the rate. However, a point is reached where all active sites are occupied; adding more substrate will have no further effect. The rate plateaus because the enzyme is the limiting factor.

如果酶浓度保持不变，增加底物浓度会使速率初期上升。但当所有活性位点都被占据后，再增加底物也没有进一步的效应。由于酶成为限制因素，速率不会继续上升。

Rate ∝ Enzyme concentration (with excess substrate) | 速率 ∝ 酶浓度（底物过量时）

8. Inhibitors | 抑制剂

Inhibitors are substances that slow down or stop enzyme activity. They can be competitive or non-competitive.

抑制剂是能减慢或阻止酶活性的物质。它们可分为竞争性抑制剂和非竞争性抑制剂。

Competitive inhibitors have a shape similar to the substrate and compete for the active site. If they occupy the active site, the substrate cannot bind. The effect can be reduced by increasing substrate concentration.

竞争性抑制剂的形状与底物相似，会与底物竞争活性位点。如果它们占据了活性位点，底物就无法结合。增加底物浓度可以减弱这种抑制作用。

Non-competitive inhibitors bind to a site other than the active site (an allosteric site) and change the shape of the enzyme, including the active site. Increasing substrate concentration does not reverse this inhibition.

非竞争性抑制剂结合在活性位点以外的位点（别构位点）上，改变酶的整体形状，包括活性位点。增加底物浓度不能逆转这种抑制。

9. Uses of Enzymes in Biotechnology | 酶在生物技术中的应用

Enzymes are widely used in industry because they are specific, efficient and work at mild temperatures. Common examples include:

酶因其专一性、高效性和温和条件下的反应而在工业上得到广泛应用。常见例子包括：

Biological washing powders use lipase and protease to break down fat and protein stains.

生物洗衣粉利用脂肪酶和蛋白酶分解脂肪和蛋白质污渍。
Amylase is used to convert starch into sugar syrup in food production.

在食品生产中，淀粉酶用于将淀粉转化为糖浆。
Pectinase is used in fruit juice production to break down pectin and increase yield.

果汁生产中利用果胶酶分解果胶，提高出汁率。
Lactase is used to produce lactose-free milk for people with lactose intolerance.

乳糖酶用于为乳糖不耐受人群生产无乳糖牛奶。

10. Investigating Enzyme Activity | 探索酶活性的实验方法

A common experiment involves catalase and hydrogen peroxide:

一个常见实验涉及过氧化氢酶和过氧化氢：

2H₂O₂ → 2H₂O + O₂

The rate of oxygen bubble production can be used to measure the rate of reaction. To investigate the effect of temperature, place the reaction mixture in water baths at different temperatures and count the bubbles released per minute.

可通过测定氧气气泡产生的速率来衡量反应速率。为探究温度的影响，可将反应混合物置于不同温度的水浴中，每分钟记录释放的气泡数。

Another technique uses the disappearance of a substrate, for example the breakdown of starch by amylase, tested with iodine solution. The time taken for iodine to stop turning blue-black can be used to calculate the reaction rate.

另一种技术是观察底物的消失，例如用碘液检测淀粉酶分解淀粉的过程。记录碘液不再变蓝黑色所需的时间，即可计算反应速率。

When investigating the effect of pH, use buffer solutions to maintain a constant pH, while keeping temperature and substrate concentration constant.

在探究 pH 的影响时，可使用缓冲液保持 pH 恒定，同时保持温度和底物浓度不变。

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Factor \| 因素	Effect on Reaction Rate \| 对反应速率的影响
Temperature \| 温度	As temperature rises, particles gain kinetic energy; rate increases up to optimum, then decreases as enzyme is denatured. \| 温度升高，粒子获得动能，速率上升至最适点；之后酶变性，速率下降。
pH \| pH	Each enzyme has an optimum pH; too high or too low alters the active site shape and denatures the enzyme. \| 每种酶都有最适 pH；过高或过低都会改变活性位点形状并使酶变性。
Enzyme concentration \| 酶浓度	Rate increases linearly until substrate becomes limiting. \| 反应速率随酶浓度线性增加，直到底物成为限制因素。
Substrate concentration \| 底物浓度	Rate increases until all active sites are occupied; further increases do not change the rate. \| 速率上升直到所有活性位点被占据；继续增加底物浓度速率不再改变。

Enzymes: Structure, Function and Applications | 酶：结构、功能与应用