Enzymes | 酶

📚 Enzymes | 酶

Enzymes are biological catalysts that speed up chemical reactions in living organisms without being consumed in the process. They are essential for life, enabling vital metabolic reactions to occur rapidly at body temperature.

酶是生物催化剂，能够在生物体内加速化学反应，而自身在过程中不被消耗。它们对生命至关重要，使重要的代谢反应能在体温条件下快速进行。

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1. What Are Enzymes? | 什么是酶

Enzymes are large protein molecules made of long chains of amino acids folded into a specific three-dimensional shape. This shape is determined by the sequence of amino acids and is crucial for the enzyme’s function.

酶是由氨基酸长链折叠成特定三维形状的大分子蛋白质。这种形状由氨基酸序列决定，并且对酶的功能至关重要。

Most enzymes are globular proteins, meaning they have a compact, roughly spherical shape. The unique structure includes an active site, a small region where substrate molecules bind and react.

大多数酶是球状蛋白质，即具有紧凑、近似球形的形状。其独特结构包括一个活性位点，即底物分子结合并发生反应的小区域。

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2. The Active Site and Specificity | 活性位点与特异性

The active site is a specific pocket or groove on the enzyme surface. Its shape and chemical properties are complementary to the substrate, the molecule upon which the enzyme acts. This is the basis of enzyme specificity.

活性位点是酶表面的特定凹陷或沟槽。其形状和化学性质与底物——即酶作用的分子——互补。这是酶特异性的基础。

Because only one type of substrate fits precisely into a given active site, each enzyme catalyses only one reaction or a very small class of reactions. For example, the enzyme catalase breaks down hydrogen peroxide into water and oxygen, but it does not act on other peroxides.

由于只有一种类型的底物能精确契合给定的活性位点，每种酶只催化一个反应或极少数相关反应。例如，过氧化氢酶将过氧化氢分解为水和氧气，但它不作用于其他过氧化物。

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3. Lock and Key vs Induced Fit Models | 锁钥模型与诱导契合模型

The lock and key model describes the active site as a rigid shape that exactly matches the substrate, like a key fitting into a lock. The enzyme is the lock, and the substrate is the key.

锁钥模型将活性位点描述为与底物完全匹配的刚性形状，就像钥匙插入锁一样。酶是锁，底物是钥匙。

The induced fit model is a more modern and accurate version. It suggests that the active site is flexible and deforms slightly when the substrate binds, improving the fit and facilitating the reaction. This induced strain helps break bonds and lower the activation energy.

诱导契合模型是更现代、更准确的版本。它认为活性位点是柔性的，在底物结合时会轻微变形，以改善契合度并促进反应。这种诱导应变有助于破坏化学键并降低活化能。

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

底物 + 酶 → 酶-底物复合物 → 酶 + 产物

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4. Enzyme-Catalysed Reactions and Activation Energy | 酶催化反应与活化能

All chemical reactions require a minimum amount of energy to start, called the activation energy. In biological systems, high activation energy would slow reactions to a standstill at normal temperatures.

所有化学反应都需要起动所需的最小能量，称为活化能。在生物系统中，高活化能会使反应在正常温度下几乎停滞。

Enzymes reduce the activation energy by providing a favourable environment within the active site. This allows more molecules to have enough energy to react, dramatically increasing the reaction rate.

酶通过提供活性位点内有利的环境来降低活化能。这使得更多分子拥有足够的能量进行反应，从而显著提高反应速率。

During the reaction, the enzyme binds to the substrate, forming an enzyme-substrate complex. Bonds in the substrate are weakened, leading to products. The enzyme remains unchanged and can be reused.

反应过程中，酶与底物结合，形成酶-底物复合物。底物中的化学键被削弱，从而生成产物。酶保持原样并可重复使用。

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5. Effect of Temperature | 温度的影响

Temperature affects enzyme activity through kinetic energy and protein stability. At low temperatures, molecules move slowly, and fewer collisions occur between enzyme and substrate, so the reaction rate is low.

温度通过分子动能和蛋白质稳定性影响酶活性。低温时，分子运动缓慢，酶与底物碰撞次数少，反应速率低。

As temperature rises, molecules gain kinetic energy, and the rate of successful collisions increases. The reaction rate therefore increases up to an optimum temperature, usually around 37°C for human enzymes.

随着温度升高，分子获得更多动能，成功碰撞的频率增加。因此反应速率上升至最适温度，人体酶通常约为37°C。

Above the optimum, the higher thermal energy breaks the hydrogen bonds and other interactions maintaining the enzyme’s three-dimensional structure. The active site changes shape, and the enzyme becomes denatured. Denaturation is permanent, and the enzyme can no longer catalyse reactions.

超过最适温度后，更高的热能破坏维持酶三维结构的氢键和其他相互作用。活性位点形状改变，酶发生变性。变性是不可逆的，酶不能再催化反应。

Q₁₀ = Rate at (T + 10°C) ÷ Rate at T

Q₁₀ = T + 10°C时的速率 ÷ T时的速率

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6. Effect of pH | pH的影响

Each enzyme has an optimum pH at which its activity is maximum. For most enzymes in the human body, this is around pH 7 (neutral), but pepsin in the stomach works best at pH 2, and trypsin in the small intestine at pH 8.

每种酶都有其活性最大的最适pH。人体大多数酶的最适pH约为7（中性），但胃中的胃蛋白酶在pH 2时活性最强，小肠中的胰蛋白酶则在pH 8时最佳。

Extreme pH values alter the charge distribution on the enzyme molecule and disrupt ionic bonds within the protein. This changes the shape of the active site, causing denaturation. The effect is often reversible if normal pH is restored quickly, but severe changes are permanent.

极端的pH值会改变酶分子上的电荷分布，并破坏蛋白质内部的离子键。这改变了活性位点的形状，导致变性。若及时恢复正常pH，影响常可逆转，但严重变化会造成永久变性。

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

When substrate concentration is fixed, increasing enzyme concentration provides more active sites, so more collisions can occur per second. The reaction rate increases proportionally as long as substrate is not limiting.

当底物浓度固定时，增加酶浓度可提供更多活性位点，因此每秒发生更多碰撞。只要底物不成为限制因素，反应速率会按比例增加。

When enzyme concentration is fixed, increasing substrate concentration initially raises the reaction rate because more substrate molecules are available to bind to active sites. However, a point is reached where all active sites are occupied; further increases in substrate do not speed up the reaction. The rate levels off at the maximum velocity (Vmax).

当酶浓度固定时，增加底物浓度最初会提高反应速率，因为更多底物分子可供活性位点结合。但会到达所有活性位点均被占用的点；继续增加底物不会加快反应。速率达到最大速度（Vmax）后不再上升。

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8. Inhibitors: Competitive and Non-competitive | 抑制剂：竞争性与非竞争性

Inhibitors are substances that reduce or stop enzyme activity. They can be competitive, non-competitive, or reversible/irreversible.

抑制剂是降低或停止酶活性的物质。它们可以是竞争性的、非竞争性的，也可以是可逆或不可逆的。

A competitive inhibitor has a shape similar to the substrate and competes for the active site. It blocks the substrate from binding. Increasing the substrate concentration can overcome competitive inhibition, because a higher substrate concentration outcompetes the inhibitor.

竞争性抑制剂的形状与底物相似，会与底物竞争活性位点。它阻止底物结合。增加底物浓度可以克服竞争性抑制，因为更高浓度的底物能胜过抑制剂。

A non-competitive inhibitor binds to a site other than the active site (an allosteric site). This changes the enzyme’s overall shape, including the active site, making it non-functional. Adding more substrate does not reverse non-competitive inhibition.

非竞争性抑制剂结合在活性位点以外的部位（别构位点）。这会改变酶的整体形状，包括活性位点，使其丧失功能。增加底物浓度无法逆转非竞争性抑制。

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9. Enzymes in Digestion | 消化中的酶

Digestive enzymes break down large insoluble food molecules into small soluble ones that can be absorbed into the bloodstream. Key examples include amylase, protease, and lipase.

消化酶将大的不溶性食物分子分解为可被吸收进入血液的小的可溶性分子。关键例子包括淀粉酶、蛋白酶和脂肪酶。

Amylase catalyses the breakdown of starch into maltose. It is produced in the salivary glands and the pancreas. Protease (such as pepsin and trypsin) breaks down proteins into amino acids. Lipase breaks down lipids into glycerol and fatty acids, often aided by bile salts.

淀粉酶催化淀粉分解为麦芽糖。它由唾液腺和胰腺产生。蛋白酶（如胃蛋白酶和胰蛋白酶）将蛋白质分解为氨基酸。脂肪酶将脂质分解为甘油和脂肪酸，且常需胆盐辅助。

Enzyme 酶	Substrate 底物	Product 产物
Amylase 淀粉酶	Starch 淀粉	Maltose 麦芽糖
Protease 蛋白酶	Protein 蛋白质	Amino acids 氨基酸
Lipase 脂肪酶	Lipids 脂质	Glycerol + Fatty acids 甘油 + 脂肪酸

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10. Industrial and Medical Uses of Enzymes | 酶的工业与医疗应用

Enzymes are widely used in biotechnology because they are specific, efficient, and environmentally friendly. In biological washing powders, proteases and lipases break down protein and fat stains at lower temperatures, saving energy.

酶因其特异性、高效性和环保性而被广泛应用于生物技术。在生物洗衣粉中，蛋白酶和脂肪酶在较低温度下分解蛋白质和脂肪污渍，从而节省能源。

In food industry, enzymes are used to clarify fruit juices (pectinase), produce syrup (invertase), and tenderise meat (papain). In medicine, enzymes help diagnose disease (e.g., glucose oxidase in test strips) and treat conditions (e.g., lactase supplements for lactose intolerance).

在食品工业中，酶用于澄清果汁（果胶酶）、生产糖浆（转化酶）和使肉变嫩（木瓜蛋白酶）。在医学中，酶用于诊断疾病（例如试纸中的葡萄糖氧化酶）和治疗疾病（例如乳糖酶补充剂用于乳糖不耐受）。

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11. Summary | 总结

Enzymes are specific biological catalysts that lower activation energy, making reactions occur rapidly under mild conditions. Their activity depends on temperature, pH, enzyme concentration, and substrate concentration, and can be regulated by inhibitors.

酶是特异性的生物催化剂，通过降低活化能，使反应在温和条件下快速发生。其活性受温度、pH、酶浓度和底物浓度影响，并可被抑制剂调节。

Understanding enzyme action is fundamental to biology, medicine, and industry. From digestion to DNA replication, enzymes drive the chemistry of life.

理解酶的作用方式是生物学、医学和工业的基础。从消化到DNA复制，酶驱动着生命的化学反应。

Published by TutorHao | Biology Revision Series | aleveler.com

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