Understanding Enzyme Activity | 酶活性解析

📚 Understanding Enzyme Activity | 酶活性解析

Enzymes are biological catalysts that speed up chemical reactions in living organisms without being used up themselves. They are essential for processes such as digestion, respiration and photosynthesis. In the IGCSE Edexcel Science syllabus, you need to understand how enzymes work and what affects their activity.

酶是生物催化剂，能在不自身损耗的情况下加速生物体内的化学反应。它们在消化、呼吸和光合作用等过程中至关重要。在IGCSE Edexcel科学课程中，你需要理解酶的作用方式以及哪些因素会影响酶活性。

1. What Are Enzymes? | 什么是酶？

Enzymes are proteins made of long chains of amino acids folded into a specific three-dimensional shape. This shape is critical because it creates an area called the active site, where the substrate binds and the reaction takes place.

酶是由氨基酸长链折叠成特定三维形状的蛋白质。这种形状至关重要，因为它构成了一个称为活性位的区域，底物在此结合并发生反应。

Enzymes are specific: each enzyme catalyses only one type of reaction.
They are reusable: an enzyme molecule can catalyse many reactions.
They lower the activation energy of a reaction.

酶具有专一性：每种酶只催化一种类型的反应。
酶可重复使用：一个酶分子可以催化许多次反应。
酶降低反应的活化能。

Substrate + Enzyme → Product + Enzyme

2. The Lock and Key Model | 锁钥模型

The ‘lock and key’ model explains enzyme specificity. The active site is the lock, and the substrate is the key. Only the correctly shaped substrate fits into the active site, like a key fitting into a lock. Once bound, the reaction occurs and products are released.

“锁钥模型”解释了酶的专一性。活性位是锁，底物是钥匙。只有形状正确的底物才能像钥匙插入锁一样进入活性位。结合后反应发生，产物被释放。

Feature	Explanation
Active site	The region where the substrate binds
Specificity	Only one substrate fits the active site
Enzyme-substrate complex	The temporary structure formed during the reaction

锁钥模型解释了酶与底物的匹配关系，其中活性位和底物像锁和钥匙一样精确互补。

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

Several factors change how fast an enzyme works. These include temperature, pH, substrate concentration and enzyme concentration. Each factor can increase, decrease or stop enzyme activity completely.

多种因素会改变酶工作的速率，包括温度、pH值、底物浓度和酶浓度。每个因素都可能提高、降低或完全停止酶活性。

Temperature: affects molecular movement and enzyme structure.
pH: affects the charge and shape of the active site.
Substrate concentration: affects how often enzymes meet substrate molecules.
Enzyme concentration: affects the number of active sites available.

温度：影响分子运动和酶结构。
pH值：影响活性位的电荷和形状。
底物浓度：影响酶与底物分子相遇的频率。
酶浓度：影响可用活性位的数量。

4. Effect of Temperature | 温度的影响

As temperature rises, molecules move faster. More enzyme-substrate collisions occur per second, so the rate of reaction increases. For most enzymes, the rate doubles for every 10 °C rise, until the optimum temperature is reached.

随着温度升高，分子运动加快，每秒内酶与底物的碰撞次数增多，因此反应速率上升。对大多数酶而言，每升高10 °C速率约翻倍，直到达到最适温度。

However, above the optimum temperature, the enzyme begins to denature. The heat breaks the weak bonds that hold the protein structure together. The active site changes shape, so the substrate can no longer fit. The enzyme is permanently inactive.

然而，超过最适温度后，酶开始变性。高温破坏维持蛋白质结构的弱键，活性位形状改变，底物无法再结合。酶永久失活。

Q₁₀ = Rate at (T + 10 °C) ÷ Rate at T

Denaturation is not the same as the enzyme being ‘killed’. Enzymes are not alive, but their shape is destroyed.

变性不等于酶“被杀”。酶并非生物，但其形状遭到破坏。

5. Effect of pH | pH值的影响

Each enzyme has an optimum pH at which its activity is highest. For most human enzymes, this is around pH 7. However, 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值，此时活性最高。大多数人源酶的最适pH约为7。但胃中的胃蛋白酶在pH 2时活性最高，而肠道中的胰蛋白酶在pH 8时活性最高。

If the pH moves too far from the optimum, the concentration of H⁺ or OH⁻ ions disrupts the ionic bonds holding the enzyme’s shape. The active site becomes distorted, and the enzyme denatures.

如果pH值偏离最适范围过大，H⁺或OH⁻离子浓度会破坏维持酶形状的离子键，导致活性位变形，酶发生变性。

Enzyme	Optimum pH	Location
Pepsin	2	Stomach
Amylase	7	Saliva / Pancreas
Trypsin	8	Small intestine

6. Effect of Substrate Concentration | 底物浓度的影响

At a fixed enzyme concentration, increasing the substrate concentration initially increases the rate of reaction. More substrate molecules mean more frequent successful collisions with active sites.

在固定酶浓度下，增加底物浓度最初会提高反应速率。更多底物分子意味着与活性位成功碰撞的频率更高。

Eventually, a point is reached where all active sites are occupied. Adding more substrate has no effect on the rate because the enzyme becomes saturated. The rate levels off on a graph.

最终会达到一个所有活性位都被占据的点。此时再添加底物不会影响速率，因为酶已达到饱和。在图表上速率趋于平缓。

Rate → Vmax (maximum velocity) at saturation

At saturation, the only way to increase the rate further is to add more enzyme molecules.

在饱和状态下，进一步提高速率的唯一方法是添加更多酶分子。

7. Effect of Enzyme Concentration | 酶浓度的影响

If substrate is present in excess, increasing the enzyme concentration increases the rate of reaction. More enzyme molecules mean more active sites available, so more substrate can be converted to product per second.

如果底物过量，增加酶浓度会提高反应速率。更多酶分子意味着更多可用活性位，因此每秒能转化更多底物为产物。

This relationship is generally directly proportional: doubling the enzyme concentration doubles the rate, as long as substrate remains in excess. Once substrate starts to run out, the rate stops increasing.

这种关系通常成正比：只要底物仍过量，酶浓度加倍则速率加倍。一旦底物开始不足，速率便停止上升。

Enzyme concentration is the limiting factor when substrate is abundant.
Substrate concentration is the limiting factor when enzyme is abundant.

底物充足时，酶浓度是限制因素。
酶充足时，底物浓度是限制因素。

8. Inhibitors | 抑制剂

Inhibitors are substances that reduce enzyme activity. They can be competitive or non-competitive. Competitive inhibitors have a similar shape to the substrate and block the active site. Increasing substrate concentration can overcome competitive inhibition.

抑制剂是降低酶活性的物质，分为竞争性抑制剂和非竞争性抑制剂。竞争性抑制剂具有与底物相似的形状，会占据活性位。增加底物浓度可以克服竞争性抑制。

Non-competitive inhibitors bind to another part of the enzyme, changing the shape of the active site so the substrate cannot bind. Adding more substrate does not help because the active site is already distorted.

非竞争性抑制剂结合在酶的其他部位，改变活性位形状使底物无法结合。增加底物没有帮助，因为活性位已被扭曲。

Type	Binding site	Effect of more substrate
Competitive	Active site	Inhibition can be reversed
Non-competitive	Allosteric site	Inhibition remains

Heavy metals such as lead and mercury act as non-competitive inhibitors for many enzymes.

铅和汞等重金属对许多酶起非竞争性抑制作用。

9. Applications of Enzymes | 酶的应用

Enzymes are widely used in industry and medicine. Understanding their optimal conditions is essential for economic efficiency.

酶在工业和医学中被广泛使用。了解其最适条件对于经济效益至关重要。

Biological detergents contain proteases and lipases to break down protein and fat stains at low temperatures.
Food industry uses pectinase to clarify fruit juices and lactase to produce lactose-free milk.
Medicine uses enzymes like streptokinase to dissolve blood clots.
Bioethanol production uses enzymes to convert starch into fermentable sugars.

生物洗涤剂含蛋白酶和脂肪酶，在低温下分解蛋白质和脂肪污渍。
食品工业使用果胶酶澄清果汁，使用乳糖酶生产无乳糖牛奶。
医学使用链激酶等酶溶解血栓。
生物乙醇生产使用酶将淀粉转化为可发酵糖。

Industrial enzymes are often immobilised on a solid support. This allows the enzymes to be reused, and products are not contaminated by the enzyme.

工业酶常被固定在固体载体上。这样酶可以重复使用，且产物不会被酶污染。

10. Summary | 总结

Enzyme activity depends on temperature, pH, substrate concentration, enzyme concentration and inhibitors. The active site is central to enzyme function. Denaturation permanently destroys enzyme activity by changing the shape of the active site.

酶活性取决于温度、pH值、底物浓度、酶浓度和抑制剂。活性位是酶功能的核心。变性通过改变活性位形状而永久破坏酶活性。

For exam success, practise interpreting graphs of reaction rate against temperature and pH. Remember that denaturation is irreversible, while saturation is reversible when substrate concentration is lowered.

为了考试成功，练习解读反应速率随温度和pH变化的图表。记住变性是不可逆的，而降低底物浓度后饱和状态可以逆转。

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Understanding Enzyme Activity | 酶活性解析