Enzymes | 酶

📚 Enzymes | 酶

Enzymes are biological catalysts that speed up chemical reactions in living organisms without being used up in the process. They are essential for metabolism, digestion, and countless cellular processes.

酶是生物催化剂，能在生物体内加速化学反应，而自身在反应过程中不被消耗。酶对代谢、消化以及无数细胞过程至关重要。

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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 of each enzyme allows it to bind only to its specific substrate.

酶是由氨基酸长链折叠成的特定三维形状的蛋白质。每种酶独特的形状使其只能与特定的底物结合。

Enzymes are highly specific. For example, amylase only breaks down starch, while protease only breaks down proteins. This specificity is often described as a ‘lock and key’ mechanism.

酶具有高度专一性。例如，淀粉酶只分解淀粉，而蛋白酶只分解蛋白质。这种专一性常被描述为“锁钥”机制。

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2. The Mechanism of Enzyme Action | 酶作用机制

In the ‘lock and key’ model, the enzyme is the lock and the substrate is the key. The substrate fits into the enzyme’s active site, forming an enzyme-substrate complex. The reaction then occurs, and the products are released, leaving the enzyme unchanged.

在“锁钥”模型中，酶是锁，底物是钥匙。底物与酶的活性位点结合，形成酶-底物复合物。随后反应发生，产物释放，酶保持不变。

An alternative model is the ‘induced fit’ model, where the active site changes shape slightly to better fit the substrate after binding. This increases the catalytic efficiency.

另一种模型是“诱导契合”模型，即结合后活性位点形状发生轻微改变以更好地契合底物，从而提高催化效率。

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

酶 + 底物 → 酶-底物复合物 → 酶 + 产物

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

The rate of an enzyme-catalysed reaction is influenced by several factors: temperature, pH, enzyme concentration, substrate concentration, and the presence of inhibitors.

酶促反应速率受多种因素影响：温度、pH、酶浓度、底物浓度以及抑制剂的存在。

• Temperature: As temperature increases, kinetic energy increases, leading to more frequent collisions between enzyme and substrate. However, above an optimum temperature, the enzyme denatures.
• 温度：温度升高，动能增加，酶与底物碰撞更频繁。但超过最适温度后，酶会变性失活。
• pH: Each enzyme has an optimum pH. Extreme pH values disrupt hydrogen bonds and alter the shape of the active site.
• pH：每种酶都有最适pH。极端pH会破坏氢键并改变活性位点的形状。
• Enzyme concentration: The rate increases with enzyme concentration, assuming substrate is in excess.
• 酶浓度：在底物过量时，反应速率随酶浓度增加而增加。
• Substrate concentration: Increasing substrate concentration increases the rate until the active sites become saturated.
• 底物浓度：增加底物浓度可提高速率，直到活性位点达到饱和。
• Inhibitors: Molecules that reduce enzyme activity by blocking or altering the active site.
• 抑制剂：通过阻断或改变活性位点来降低酶活性的分子。

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4. Temperature and Enzyme Activity | 温度与酶活性

Enzyme activity increases with temperature up to an optimum point, usually around 37 °C for human enzymes. The rate of reaction roughly doubles for every 10 °C rise, until the optimum.

酶活性随温度升高而增强，达到最适温度（人体酶通常约为37 °C）后开始下降。在低于最适温度时，温度每升高10 °C，反应速率大约增加一倍。

Above the optimum temperature, the enzyme’s structure begins to unfold. This is called denaturation. The active site loses its shape, and the enzyme can no longer catalyse the reaction. Denaturation is usually irreversible.

超过最适温度，酶的结构开始解折叠，称为变性。活性位点失去原有形状，酶无法再催化反应。变性通常不可逆。

Optimum temperature ≈ 37 °C (human enzymes)

最适温度 ≈ 37 °C（人体酶）

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5. pH and Enzyme Activity | pH与酶活性

Each enzyme has an optimum pH at which it works best. For example, pepsin in the stomach works best at pH 2, while trypsin in the intestine works best at pH 8.

每种酶都有一个最适pH。例如，胃中的胃蛋白酶在pH 2时活性最高，而肠中的胰蛋白酶在pH 8时活性最高。

If the pH deviates too far from the optimum, hydrogen bonds within the enzyme are disrupted, changing the shape of the active site. The enzyme denatures and loses its function.

如果pH偏离最适值过远，酶内部的氢键会被破坏，改变活性位点的形状，导致酶变性失活。

• Pepsin: optimum pH 1.5 – 2.5 (stomach)
• 胃蛋白酶：最适pH 1.5 – 2.5（胃部）
• Amylase: optimum pH 7.0 (saliva and pancreas)
• 淀粉酶：最适pH 7.0（唾液和胰腺）
• Trypsin: optimum pH 8.0 (small intestine)
• 胰蛋白酶：最适pH 8.0（小肠）

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

When substrate concentration is fixed and enzyme concentration is increased, the rate of reaction increases proportionally because more active sites are available. However, if enzyme concentration is fixed and substrate concentration is increased, the rate increases until the enzyme’s active sites are fully occupied.

当底物浓度固定而增加酶浓度时，反应速率成比例增加，因为可用活性位点增多。然而，当酶浓度固定而增加底物浓度时，速率增加到所有活性位点都被占据为止。

At the plateau phase, all enzyme molecules are saturated with substrate. Further addition of substrate has no effect on the rate. The only way to increase the rate further is to add more enzyme.

在平台期，所有酶分子都被底物饱和。此时再增加底物不影响速率。进一步提高速率的唯一方法是增加酶量。

V_max = maximum rate when all active sites are occupied

V_max = 所有活性位点被占据时的最大速率

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7. Inhibitors | 抑制剂

Inhibitors are substances that reduce or stop enzyme activity. There are two main types: competitive and non-competitive inhibitors.

抑制剂是能降低或停止酶活性的物质，主要分为竞争性抑制剂和非竞争性抑制剂两类。

Competitive inhibitors have a similar shape to the substrate and compete for the active site. They block the substrate from binding. Increasing substrate concentration can overcome competitive inhibition.

竞争性抑制剂具有与底物相似的形状，与底物竞争活性位点，阻止底物结合。增加底物浓度可克服竞争性抑制。

Non-competitive inhibitors bind to an allosteric site (a site other than the active site), changing the shape of the enzyme. This prevents the substrate from binding even if substrate concentration is high. Non-competitive inhibition is often irreversible.

非竞争性抑制剂结合到变构位点（非活性位点的其他位置），改变酶的形状，使得底物无法结合，即使底物浓度很高也无法逆转。非竞争性抑制通常不可逆。

Feature	Competitive	Non-competitive
Binds to	Active site	Allosteric site
Effect on V_max	No change (if substrate overcomes)	Decreases
Overcome by more substrate?	Yes	No

Competitive inhibition: E + I ⇌ EI (reversible) | Non-competitive: E + I → EI (irreversible)

竞争性抑制：E + I ⇌ EI（可逆）| 非竞争性：E + I → EI（不可逆）

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8. Applications of Enzymes | 酶的应用

Enzymes are widely used in industry and medicine due to their specificity and efficiency under mild conditions.

酶因其专一性和温和条件下的高效性，被广泛用于工业和医疗领域。

• Biological washing powders: contain proteases and lipases to break down protein and fat stains.
• 生物洗衣粉：含蛋白酶和脂肪酶，分解蛋白质和脂肪污渍。
• Food industry: amylase converts starch to sugar for syrups; pectinase clarifies fruit juice.
• 食品工业：淀粉酶将淀粉转化为糖浆；果胶酶使果汁澄清。
• Medicine: enzymes are used to diagnose diseases (e.g., glucose biosensors for diabetes) and to treat enzyme deficiencies.
• 医学：酶用于疾病诊断（如糖尿病血糖生物传感器）和治疗酶缺乏症。
• Molecular biology: restriction enzymes cut DNA for genetic engineering.
• 分子生物学：限制性内切酶切割DNA用于基因工程。

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9. Immobilised Enzymes | 固定化酶

Immobilised enzymes are enzymes attached to an inert support material, such as alginate beads or silica gel. This allows them to be reused and easily separated from the product.

固定化酶是附着在惰性载体材料（如海藻酸钙珠或硅胶）上的酶，可以重复使用并易于与产物分离。

Advantages include:

优点包括：

• Enzymes can be reused, reducing cost.
• 酶可重复使用，降低成本。
• Products are free from enzyme contamination, improving quality.
• 产物不含酶，提高纯度。
• Greater stability to temperature and pH changes.
• 对温度和pH变化的稳定性更高。
• Continuous processes are possible, e.g., in bioreactors.
• 可实现连续化生产，如生物反应器中的应用。

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10. Summary | 总结

Enzymes are vital biological catalysts with high specificity. Their activity is influenced by temperature, pH, enzyme concentration, substrate concentration, and inhibitors. Understanding how enzymes work and what affects them is crucial for biology, medicine, and biotechnology.

酶是重要的生物催化剂，具有高度专一性。其活性受温度、pH、酶浓度、底物浓度和抑制剂的影响。理解酶的作用方式及其影响因素，对生物学、医学和生物技术至关重要。

Remember the key concepts:

记住关键概念：

• Enzymes are proteins with an active site that binds to a specific substrate.
• 酶是含有活性位点的蛋白质，与特定底物结合。
• Temperature and pH extremes cause denaturation.
• 极端温度和pH会导致酶变性。
• Reaction rate can be increased by raising enzyme or substrate concentration until saturation.
• 反应速率可通过增加酶或底物浓度提高，直到饱和。
• Inhibitors reduce enzyme activity, and their effect depends on type.
• 抑制剂降低酶活性，其作用方式取决于类型。

Enzymes = Biological Catalysts | 酶 = 生物催化剂

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