Enzymes: The Biological Catalysts | 酶：生物催化剂

📚 Enzymes: The Biological Catalysts | 酶：生物催化剂

Enzymes are protein molecules that act as biological catalysts, speeding up chemical reactions in living organisms without being used up. They are essential for nearly every metabolic process, from digestion to DNA replication.

酶是一种蛋白质分子，作为生物催化剂，在不被消耗的前提下加速生物体内的化学反应。从消化到DNA复制，几乎每一个代谢过程都离不开酶。

1. What Are Enzymes? | 什么是酶？

Enzymes are large, complex proteins with a specific three-dimensional shape. They lower the activation energy of a reaction, allowing reactions to occur rapidly at normal body temperatures, typically 37 °C in humans.

酶是体积大且结构复杂的蛋白质，具有特定的三维形状。它们能降低反应的活化能，使反应在正常体温（人类约为37 °C）下迅速进行。

Each enzyme is highly specific, meaning it only catalyses one type of reaction or acts on one type of substrate. For example, amylase only breaks down starch, not protein or fat.

每种酶都具有高度特异性，即只催化一种类型的反应或只作用于一种底物。例如，淀粉酶只能分解淀粉，不能分解蛋白质或脂肪。

Biological catalyst – accelerates reactions without being changed.
生物催化剂 – 加速反应而不发生自身改变。
Globular protein – folded into a specific shape, often water-soluble.
球状蛋白质 – 折叠成特定形状，通常可溶于水。

2. Structure of Enzymes | 酶的结构

Enzymes are made of chains of amino acids folded into complex shapes. The unique sequence and folding create an active site, a small region where the substrate binds. The shape of the active site is complementary to the shape of the substrate molecule.

酶由氨基酸链折叠成复杂形状。独特的氨基酸序列和折叠方式形成了一个活性位点，即底物结合的小区域。活性位点的形状与底物分子的形状互补。

The specificity of an enzyme depends entirely on the geometry of its active site. If the active site changes shape, the enzyme may no longer function. This is called denaturation, which can be caused by high temperature or extreme pH.

酶的特异性完全取决于其活性位点的几何结构。如果活性位点形状改变，酶可能失去功能。这种情况称为变性，可由高温或极端pH引起。

3. The Lock and Key Hypothesis | 锁钥模型

The lock and key hypothesis explains how enzymes work. The enzyme is the lock, and the substrate is the key. Only the correct key (substrate) fits into the lock (active site), forming an enzyme-substrate complex.

锁钥模型解释了酶的作用方式。酶是锁，底物是钥匙。只有正确的钥匙（底物）才能插入锁（活性位点）中，形成酶-底物复合物。

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

酶 + 底物 → 酶-底物复合物 → 酶 + 产物

This model shows that the active site is rigid and perfectly shaped for one substrate. However, a more accurate model is the induced fit hypothesis, which suggests the active site slightly changes shape to better fit the substrate.

该模型表明活性位点是刚性的，且形状只完美匹配一种底物。然而，更准确的是诱导契合模型，它认为活性位点会略微改变形状以更好地结合底物。

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

Several factors influence how quickly an enzyme-catalysed reaction proceeds. The most important are temperature, pH, enzyme concentration, and substrate concentration. Each factor affects the frequency and success of enzyme-substrate collisions.

影响酶促反应速率的因素有很多，最重要的是温度、pH、酶浓度和底物浓度。每个因素都影响酶与底物碰撞的频率和成功率。

Altering these factors can increase or decrease the rate until an optimum is reached. Beyond the optimum, the enzyme may become denatured, losing its shape permanently.

改变这些因素可以在达到最适条件前提高或降低反应速率。而一旦超过最适条件，酶可能变性，永久失去其形状。

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

As temperature increases, molecules move faster, so enzymes and substrates collide more frequently. The rate of reaction therefore increases up to the optimum temperature, usually around 40 °C in the human body.

随着温度升高，分子运动加快，酶与底物碰撞更加频繁，因此反应速率上升，直到达到最适温度，人体内通常约为40 °C。

Above the optimum temperature, vibrations inside the enzyme molecule break the bonds holding the structure together. The active site changes shape and the enzyme is said to be denatured. Denaturation is permanent.

超过最适温度后，酶分子内部的振动会破坏维持结构的化学键，导致活性位点形状改变，酶即发生变性。变性是不可逆的。

Temperature	Effect on Rate
Low (0 °C)	Very slow – molecules have low kinetic energy
Optimum (40 °C)	Maximum rate – most frequent successful collisions
High (>45 °C)	Denaturation – active site loses shape

6. pH and Enzyme Activity | pH与酶活性

Each enzyme has an optimum pH at which it works best. Most enzymes in the human body function optimally around pH 7, but pepsin in the stomach works best at pH 2, the acidic environment there.

每种酶都有一个最适pH，在此pH下活性最高。人体内大多数酶的最适pH接近7，但胃中的胃蛋白酶在pH 2的酸性环境中活性最佳。

Changes in pH affect the charges on amino acid residues in the enzyme, altering the hydrogen bonds and ionic bonds that maintain its shape. Extremes of pH can denature the enzyme, just like high temperature does.

pH变化会影响酶中氨基酸残基的电荷，改变维持其形状的氢键和离子键。极端pH会导致酶变性，就像高温一样。

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

When enzyme concentration increases, there are more active sites available, so more substrate molecules can be converted per unit time. This results in a linear increase in rate, as long as enough substrate is present.

酶浓度增加时，活性位点数量增多，单位时间内可转化的底物分子更多。只要底物充足，反应速率会呈线性增加。

Substrate concentration affects rate in a different way. Initially, adding more substrate increases the rate because more enzyme-substrate complexes can form. However, once all enzyme active sites are occupied, the rate reaches a plateau. Adding more substrate has no further effect unless enzyme concentration also increases.

底物浓度对速率的影响不同。最初，增加底物浓度会加快反应，因为能形成更多酶-底物复合物。然而，当所有酶活性位点都被占据时，速率达到平台期。此时再增加底物也不再提高速率，除非同时增加酶浓度。

Enzyme concentration – rate increases linearly (substrate unlimited).
酶浓度 – 速率线性增加（底物不限）。
Substrate concentration – rate rises then plateaus.
底物浓度 – 速率先升高后趋于平稳。

8. Inhibitors | 抑制剂

Inhibitors are substances that reduce the rate of an enzyme-catalysed reaction. They can be competitive or non-competitive. Competitive inhibitors have a similar shape to the substrate and compete for the active site, blocking it temporarily.

抑制剂是能降低酶促反应速率的物质，分为竞争性抑制剂和非竞争性抑制剂。竞争性抑制剂的形状与底物相似，会与底物竞争活性位点，临时占据它。

Non-competitive inhibitors bind to a site other than the active site (an allosteric site) and change the shape of the enzyme, so the active site no longer fits the substrate. This inhibition cannot be overcome by adding more substrate.

非竞争性抑制剂结合在活性位点以外的部位（别构位点），改变酶的形状，使活性位点不能再匹配底物。这种抑制无法通过增加底物浓度来解除。

9. Applications of Enzymes | 酶的应用

Enzymes are widely used in industry and medicine. For example, amylase and maltase are used to convert starch into glucose syrup; proteases are used in biological washing powders to break down protein stains; and lipases are used in making cheese and removing fats.

酶在工业和医疗领域应用广泛。例如，淀粉酶和麦芽糖酶用于将淀粉转化为葡萄糖浆；蛋白酶用于加酶洗衣粉分解蛋白污渍；脂肪酶用于制作奶酪和去除油脂。

Enzymes are beneficial in industrial processes because they work at moderate temperatures and pH, reducing energy costs and reducing the need for harsh chemicals. However, they can be sensitive to changes in conditions and may be expensive to produce in purified form.

酶在工业中具有优势，因为它们在温和的温度和pH条件下工作，降低能源成本并减少使用烈性化学品。然而，酶对条件变化敏感，且纯化酶的成本可能较高。

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Enzymes: The Biological Catalysts | 酶：生物催化剂