Name: enzyme action and inhibition
Uploaded: 2020-09-24T15:06:50.000Z
Duration: 2 min 34 s
Channel: JoVE

K12 Standards

north-carolina-k-12-science-standard-course-of-study

NC K-12 Science Standard Course of Study

9-12

Chemistry

Matter and its Interactions

PS.Chm.5.1

Enzymes

酵素は、生化学反応の速度を加速する生物学的触媒です。ほとんどの酵素はタンパク質であり、アミノ酸で構成されています。一部はリボザイムとして知られるRNA分子です。 
酵素は、反応の活性化エネルギーを低下させることで作用し、それによって反応速度を増加させます。それらは化学結合の合成と分解の両方を触媒することができますが、反応の方向や平衡に影響を与えません。 
各酵素は、基質と呼ばれる特定の反応物に結合し、特定の反応を触媒します。この基質は、分子間力や一過性共有結合などの相互作用を通じて、活性部位と呼ばれる酵素の明確な触媒領域に結合し、酵素-基質複合体を形成します。
この結合は、酵素とその基質との間に必要なコンフォメーション相補性により、非常に特異的です。したがって、特定の酵素は、そのコンフォメーションに基づいてのみ特定の反応を触媒することができます。 
複合体形成を理解する簡単な方法は、ロックアンドキーモデルであり、これは、基質が酵素の活性部位に収まると仮定し、対応する「ロック」に適合する「キー」に似ています。 
ただし、別のモデルである誘導フィットモデルでは、複合体の動的性質が考慮されます。このモデルでは、基質が結合すると、小さなコンフォメーション変化が誘発され、その結果、反応に有利なより緊密な適合が得られると述べています。 
反応の活性化エネルギーは、さまざまな方法で下げることができます。 
一般的なメカニズムには、基質のコンフォメーション変化を誘発して結合をより簡単に切断できるようにすることや、2つの基質の反応性基を近接させて結合形成を促進することなどがあります。酵素活性は、阻害剤と呼ばれる天然分子または合成分子によって一時的または永続的に抑制できます。
例えば、競合阻害剤は、基質と競合して酵素の活性部位に結合するため、基質の結合が妨げられます。
一方、非競合阻害剤は酵素上の別の場所に結合し、活性部位で構造変化を引き起こし、酵素の触媒活性を低下させます。

酵素

生体内において、酵素は細胞代謝に関与する多くの生化学反応の触媒として機能します。酵素の役割は、その基質と複合体を形成することにより、生化学反応の活性化エネルギーを低下させることです。活性化エネルギーの低下は、生化学反応の速度を増加させます。
 酵素が欠乏すると、生命を脅かす病気につながることがよくあります。例えば、酵素G6PD（グルコース-6-リン酸デヒドロゲナーゼ）の欠損をもたらす遺伝的異常は、NADPHを細胞に供給する代謝経路に悪影響を及ぼす。
 この代謝経路の崩壊は、赤血球中のグルタチオンを減少させ、ヘモグロビンのような他の酵素やタンパク質に損傷を与える可能性があります。ヘモグロビンの過剰な代謝はビリルビンレベルを高め、黄疸を引き起こす。したがって、G6PD欠損症に苦しむ人々は、グルタチオン欠損赤血球に損傷を与える可能性のある化学物質を含む特定の食品や医薬品を避ける必要があります。
 酵素の機能と構造
 酵素は、その特定の機能に基づいて、さまざまな種類に分類されます。例えば、オキシドレダクターゼは酸化還元反応に関与し、トランスフェラーゼは官能基の転移を触媒します。 ATP加水分解による結合形成にはリガーゼが必要ですが、加水分解反応と二重結合形成は、それぞれ加水分解酵素とリアーゼによって触媒されます。イソメラーゼ酵素は通常、異性化反応を触媒します。
 酵素は一般的に活性部位を持ちます。これらは、酵素が特定の基質（反応物分子）に結合して酵素-基質複合体または反応中間体を形成するのに有利な配置となるような、分子上の特定の領域です。
 2つのモデル—鍵と鍵穴モデルと誘導適合モデル—は、活性部位の働きを説明する（Figure 1）。最も単純な鍵と鍵穴モデルは、活性部位と基質の分子形状が相補的であり、鍵穴と鍵のように組み合わさることを示す（Figure 1a）。一方、誘導適合モデルは、酵素分子が柔軟で、基質との結合に対応するために形状が変化することを示します。（Figure 1b）
 ただし、鍵と鍵穴モデルと誘導適合モデルはどちらも、酵素が特定の基質とのみ結合でき、特定の反応のみを触媒するという事実を示しています。
 <img alt="Eq1" src="/files/ftp_upload/11384/11384_Image_1.png" style="text-align: center; height: 300px;" />
 Figure 1 （a）鍵と鍵穴モデルによると、酵素の活性部位の形状は基質に完全に適合します。 （b）誘導適合モデルによると、活性部位は柔軟性があり、基板と結合するために形状を変えることができます。
 酵素阻害剤
 酵素の活性は、酵素阻害のプロセスによって中断される可能性があります。酵素阻害にはいくつかの種類があります。
 競合阻害プロセスでは、基質以外の分子が酵素の活性部位に直接結合します。阻害剤の基質に対する構造的および化学的類似性は、活性部位への結合を促進します。したがって、そのような競合阻害剤は基質と競合し、それらが酵素に結合するのを妨げます。ほとんどの場合、基質濃度を上げると、競合阻害の影響を抑えることができます。
 非競合的阻害では、分子は、その活性部位とは異なり、酵素のアロステリック（その他）領域に結合します。阻害剤の結合は、酵素の活性部位の配座変化を引き起こし、結果として反応を触媒する酵素の作用が低下します。競合阻害とは異なり、基質濃度の増加は非競合阻害の阻害効果を軽減しません。
 上記の文章は以下から引用しました。<a href="https://openstax.org/books/chemistry-2e/pages/12-7-catalysis">Openstax, Chemistry 2e, Section 12.7: Catalysis.</a>

生体内では、酵素は細胞代謝に関与する多くの生化学反応の触媒として作用します。酵素の役割は、...

Education

JoVE Core

化学

Chemical Kinetics

化学反応速度論

KEY TERMS AND CONCEPTS

主要用語と概念

enzyme action and inhibition

Enzymes are biological catalysts that speed up many reactions in living organisms. They help control cellular metabolism by lowering the activation energy needed for biochemical reactions. When activation energy drops, reaction rates can increase.

Enzyme problems can also lead to serious disease. A genetic abnormality that causes G6PD, or glucose-6-phosphate dehydrogenase, deficiency can disrupt the pathway that supplies NADPH to cells. In red blood cells, this can reduce glutathione and damage other enzymes and proteins such as hemoglobin. As hemoglobin is broken down too much, bilirubin builds up and can cause jaundice. People with G6PD deficiency often need to avoid certain foods and medicines that may trigger damage to their red blood cells.

Enzymes are grouped by the reactions they carry out. Oxidoreductases take part in redox reactions. Transferases move functional groups from one molecule to another. Ligases form bonds and use ATP hydrolysis, while hydrolases drive hydrolysis reactions and lyases help form double bonds. Isomerases catalyze isomerization reactions.

Most enzymes have an active site, which is the region that binds a specific substrate, or reactant molecule. The enzyme and substrate form an enzyme-substrate complex, which acts as the reaction intermediate. Two models explain how this binding works. In the lock-and-key model, the active site and substrate fit together like a key in a lock. In the induced-fit model, the enzyme changes shape to fit the substrate. Both models explain enzyme specificity, meaning an enzyme usually binds only certain substrates and catalyzes only one particular reaction.

Enzyme activity can also be blocked by inhibitors. In competitive inhibition, an inhibitor that is similar to the substrate binds directly to the active site and competes with the substrate. Increasing substrate concentration can often reduce this effect. In non-competitive inhibition, the inhibitor binds to an allosteric site, which is a different region of the enzyme. This binding changes the shape of the active site and lowers enzyme activity. Unlike competitive inhibition, adding more substrate does not fix non-competitive inhibition.

Enzyme Action and Inhibition

reaction rate

Measuring Reaction Rates

Measuring reaction rates shows how fast reactants are used up or products are formed over time. The rate of reaction is the change in the amount of a reactant or product per unit time. Because of that, scientists measure how a property changes as the reaction proceeds and connect that change to reactant or product amounts. For reactions that make or use a gas, the rate can be followed by changes in volume or pressure. A rate expression is the mathematical way to write how concentration changes...

measuring reaction rates

Tracking Reaction Kinetics with Light and Pressure

Reaction kinetics can be tracked with polarimetry, spectrometry, and pressure measurements. These methods let scientists follow a reaction without disturbing the sample. They also help determine how reactant or product concentrations change over time. Polarimetry is used for optically active substances. These substances rotate the plane of polarized light, which is called optical rotation. The effect comes from molecular structure. Normal monochromatic light is unpolarized, but after it passes...

concentration and rate law

Reaction Order from Concentration

Reaction order from concentration shows how reactant amounts affect reaction rate. Rate laws, also called differential rate laws or rate equations, are mathematical expressions that connect reaction rate with the concentrations of reactants. For a generic reaction a A + b B → products, the rate law can be written using the reactant concentrations [A] and [B] and a rate constant k. In a rate law, k is the rate constant for one specific reaction at one specific temperature. The exponents m and n...

determining order of reaction

Finding Rate Law from Initial Rates

Rate laws connect the speed of a chemical reaction to the concentration of its reactants. The rate constant, k, and the reaction orders are not taken from the chemical equation. They are found experimentally by watching how the rate changes when the reactant concentrations change. One common way to do this is the method of initial rates. In this method, several trials are run with different starting concentrations. The measured rates are then compared to determine the reaction orders and,...

the integrated rate law: the dependence of concentration on time

the-integrated-rate-law-the-dependence-of-concentration-on-time

Reading Reaction Progress with Integrated Laws

Integrated rate laws connect reaction concentration to time. They help show how much reactant or product is present after a certain period. They can also help estimate how long a reaction must run to reach a given extent. A common use is finding how long radioactive material must be stored before its radioactivity drops to a safe level. These equations come from the differential rate law after it is integrated with respect to time. For a first-order reaction, where rate = k[A], the integrated...

half-life of a reaction

Reaction Half-Life in Kinetics

Reaction half-life is the time needed for half of a reactant to be consumed. After each half-life, half of the remaining reactant is used up. A hydrogen peroxide decomposition example shows this pattern clearly. The concentration drops from 1.000 M to 0.500 M in the first 6.00 hours, then to 0.250 M in the next 6.00 hours, and then to 0.125 M in the third period. Each later 6.00-hour interval removes half of what is left. For first-order reactions, the half-life does not depend on the reactant...

temperature dependence on reaction rate

Collision Theory and Reaction Speed

Collision theory explains why reaction speed depends on how particles collide. Atoms, molecules, or ions must come close together before they can react. The theory says the reaction rate depends on the collision rate, the orientation of the colliding species, and whether the collision has enough energy for bonds to change. A gas-phase reaction between carbon monoxide and oxygen shows why orientation matters. The molecules can collide in more than one way. If the oxygen side of carbon monoxide...

arrhenius plots

Determining Activation Energy from Temperature

The Arrhenius equation links activation energy and the rate constant, k, for chemical reactions. It is written as k = Ae−Ea/RT. In this equation, R is the ideal gas constant with a value of 8.314 J/mol·K, T is the temperature on the kelvin scale, Ea is the activation energy in J/mole, e is the constant 2.7183, and A is the frequency factor. The frequency factor depends on collision frequency and the orientation of reacting molecules. Experimental kinetic data can be used to find the activation...

reaction mechanisms

Elementary Steps in Reaction Mechanisms

Chemical reactions can happen in steps, and a balanced equation does not show the full path at the molecular level. A reaction mechanism, also called a reaction path, gives the step-by-step process that explains how reactants become products. The decomposition of ozone is one example of a reaction that can be described by a sequence of steps. Each step in a mechanism is an elementary reaction. These elementary reactions happen in order, and when they are added together, they give the balanced...

rate-determining steps

Reaction Bottlenecks in Chemical Kinetics

Reaction bottlenecks help explain rate-determining steps in multistep reaction mechanisms. In a mechanism with several elementary steps, one step is often much slower than the others. That slowest step is called the rate-limiting step, or rate-determining step. A reaction cannot move faster than its slowest step, so this step controls the overall reaction rate. The idea is like traffic on a four-lane freeway with one lane closed. Cars can only move as fast as the bottleneck allows. In the same...

catalysis

Catalyst Action in Reaction Rates

Catalysts change the rate of a chemical reaction by giving it a faster path. A catalyst increases reaction rate without being consumed during the process. Its effect is often explained with reaction mechanisms and energy diagrams. For an endothermic reaction, the reactants and products start and end at the same energies in both cases. The uncatalyzed path is a one-step mechanism with one transition state. The catalyzed path follows a different mechanism with two transition states and a lower...

enzymes

Enzymes are biological catalysts that speed up many reactions in living organisms. They help control cellular metabolism by lowering the activation energy needed for biochemical reactions. When activation energy drops, reaction rates can increase. Enzyme problems can also lead to serious disease. A genetic abnormality that causes G6PD, or glucose-6-phosphate dehydrogenase, deficiency can disrupt the pathway that supplies NADPH to cells. In red blood cells, this can reduce glutathione and...

key terms and concepts

Explore how enzymes speed reactions, how active sites work, and how competitive and non-competitive inhibitors affect enzyme activity in high school biology.

Enzyme Action and Inhibition | JoVE K12

chemistry

JoVE Core 化学は、簡潔で理解しやすいアニメーションビデオレッスンを使用して、一般的な化学の概念を生き生きとしたものにします。さらに、活動する科学者のビデオでは、現在世界中の実験室で行われている古典的そして独創的な研究・実験をお見せします。

Pennsylvania State Academic Standards

Physical Science

Chemical Reactions

3.2.9-12.D

3.2.9-12.E

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

Interactions Of Matter

Chemical reactions

Virginia  Standards of Learning

HIgh School

CH.7

CH.7.f

Arizona Science Standards

High School

HS.P1

HS.P1U1.3

Next Generation Science Standards

Matter and Its Interactions

HS-PS1-4

HS-PS1-5

Florida Department of Education

SC.912.P.12

SC.912.P.12.12

Scientific Laws and Theories

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Subatomic Particles

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PS.Chm.1.1

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Nuclear Binding Energy

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Radioactive Decay and Radiometric Dating

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Nuclear Fission

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Nuclear Power

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Nuclear Fusion

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Nuclear Transmutation

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PS.Chm.1.2

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The Pauli Exclusion Principle

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The Energies of Atomic Orbitals

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PS.Chm.1.3

Periodic Classification of the Elements

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The Periodic Table

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Atomic Mass

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Molar Mass

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Use the Periodic Table as a model to predict the relative properties of elements based on the pattern of valence electrons in the outermost energy levels of atoms.

PS.Chm.2.1

atomic-radii-and-effective-nuclear-charge

Atomic Radii and Effective Nuclear Charge

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Ionic Radii

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Ionization Energy

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Electron Affinity

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Construct an explanation to infer the atomic size, reactivity, electronegativity, and ionization energy of an element based on its position in the Periodic Table.

PS.Chm.2.2

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Lewis Symbols and the Octet Rule

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Ionic Bonding and Electron Transfer

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The Born-Haber Cycle

Lattice Energy&#xA0;

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Trends in Lattice Energy: Ion Size and Charge

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Covalent Bonding and Lewis Structures

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Resonance

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Formal Charges

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Exceptions to the Octet Rule

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	...

Bond Energies and Bond Lengths

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Analyze and interpret data to explain the mechanisms and properties of the two main types of intramolecular (ionic and covalent) bonds.

PS.Chm.3.1

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Intermolecular vs Intramolecular Forces

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Intermolecular Forces

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Surface Tension, Capillary Action, and Viscosity

Surface Tension
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Construct an explanation to summarize the influences intermolecular forces have on the properties of chemical compounds.

PS.Chm.3.2

Analyze the structure of atoms and isotopes.

Enzyme Action and Inhibition

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