Name: enzyme helpers: metals, vitamins, and more
Uploaded: 2019-07-31T14:21:57.000Z
Duration: 1 min 27 s
Channel: JoVE

酵素が機能するには、多くの場合 補助因子と呼ばれるさらなる分子が必要です。この補助の働きをする分子は、金属イオン もしくは非タンパクの有機分子に分けられます。例えば、解糖の最初の段階で 補助因子のマグネシウムがATPに結合し 2つのリン酸基の結合を強化します。この作用により残りのリン酸基が 酵素であるヘキソキナーゼによって容易に切り離され グルコースをグルコース-6-リン酸に変換します。したがって、マグネシウムは補助因子としてATPに結合し その効率性を高めます。もう一つの補助因子のサブセット、補酵素は 有機化合物で、通常、ビタミンの誘導体です。例えば、ビタミンCはタンパク質であるコラーゲンの 合成に重要な補酵素です。コラーゲンがその酵素のヒドロキシラーゼに結合すると ビタミンCは酵素に結合し ヒドロキシル基を提供します。加水分解されたヒドロキシラーゼは コラーゲンが、重要な体組織の維持に不可欠である 最終的な三重螺旋構造に 変換するのを助けます。

「ビオチン依存性カルボキシラーゼの構造と機能」 Cellular and Molecular Life Sciences 70, no. 5 (2013): 863-891.[<a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3508090/">ソース</a>]

Yang, Wei, Jae Young Lee, and Marcin Nowotny. "Making and breaking nucleic acids: two-Mg2+-ion catalysis and substrate specificity." Molecular Cell 22, no. 1 (2006): 5-13.[<a href="https://doi.org/10.1016/j.molcel.2006.03.013">出典</a>]

補因子と補酵素

Cofactors and Coenzymes

酵素が正しく機能するためには、追加の成分が必要です。そのような分子には、補因子と補酵素の2種類があります。補因子は金属イオンで、補酵素は非タンパク質の有機分子です。補酵素は金属イオンで、補酵素は非タンパク質の有機分子です。これらの分子は、酵素にしっかりと結合している場合と、基質が結合したときにのみ結合する場合があります。
 
 補酵素は、成熟したタンパク質の約30%に存在し、酵素が折り畳まれる際に頻繁に取り込まれ、酵素の触媒作用に関与します。マグネシウムは、DNAポリメラーゼを含む300種類以上の酵素の必須補酵素です。この場合、マグネシウムイオンは、DNA骨格上のホスホジエステル結合の形成を助けます。その他、鉄、銅、コバルト、マンガンなどがあります。
 
 ビタミンの多くは、酵素を助ける非タンパク質の有機分子である補酵素です。例えば、ビタミンB群の一種であるビオチンは、二酸化炭素をある分子から別の分子に移動させる様々な酵素に重要な役割を果たしています。ビオチンやビタミンAなどのビタミン類は、人間の細胞では作ることができないため、食事で摂取する必要があります。

酵素が適切に機能するためには、追加の成分が必要です。分子には、補因子と補酵素の2つのクラスがあります。補因子は金属イオンです...

Education

JoVE Core

Biology

生物学

Cellular Processes

細胞プロセス

Metabolism

代謝

KEY TERMS AND CONCEPTS

主要用語と概念

enzyme helpers: metals, vitamins, and more

Enzyme helpers are needed for many enzymes to work properly. These helpers fall into two groups: cofactors and coenzymes. Cofactors are metallic ions, while coenzymes are non-protein organic molecules. Both can be tightly bound to an enzyme or attach only when the substrate binds.

Cofactors are common in mature proteins, appearing in about 30% of them. They are often added as the enzyme folds and help with catalytic activity. Magnesium is one important cofactor, and it is needed by more than 300 enzymes in the human body, including DNA polymerase. In DNA polymerase, magnesium helps form the phosphodiester bond in the DNA backbone. Iron, copper, cobalt, and manganese are other common cofactors.

Many coenzymes come from vitamins. These organic helper molecules assist enzymes during reactions. Biotin, which is a B vitamin, helps several enzymes move carbon dioxide from one molecule to another. Vitamin A and other vitamins must come from the diet because human cells cannot make them.

Enzyme Helpers: Metals, Vitamins, and More

what is metabolism?

Metabolism, Energy, and Cell Reactions

Metabolism is the set of chemical reactions that happen in a cell. It includes anabolism, which builds molecules, and catabolism, which breaks them down. These reactions help cells manage energy and keep life processes running. Cells use metabolism to turn food into energy, make cell parts, and remove waste products. Food stores potential energy in the bonds between atoms. Catabolic pathways break large food molecules into smaller ones and release that energy. Anabolic pathways use that energy...

first law of thermodynamics

Energy Flow in a Food Web

Energy flow in a food web shows the First Law of Thermodynamics in action. Energy cannot be created or destroyed. It can only change form as it moves through living things and the environment. Sunlight is the starting point. Plants capture radiant energy from the sun during photosynthesis and turn it into chemical energy stored in complex carbohydrates. At the same time, oxygen is released into the atmosphere. Herbivores eat the plants and use those sugars during digestion. The energy is...

second law of thermodynamics

Entropy in Food Web Energy Flow

The Second Law of Thermodynamics explains why entropy increases as energy moves through a system. Entropy means the amount of disorder in a system. Each time energy is transferred or transformed, some energy is lost as unusable heat. That heat can raise the motion of nearby molecules for a short time and make the surroundings less ordered and more random. This idea also appears in a food web. Primary producers, such as plants, take in energy from the sun and make food. During this process,...

kinetic energy

Motion as a Source of Energy

Kinetic energy is the energy of motion. It appears when an object is moving and can do work or cause change. A waterfall is one clear example. Water behind a dam has potential energy, but when it rushes downward, that moving water has kinetic energy. When the water reaches the bottom and stops moving, its energy can become potential energy again. Kinetic energy also shows up in living systems. Plants absorb light particles, called photons, which move very fast and help create chemical energy...

potential energy

Stored Energy in Motion and Bonds

Stored energy in motion and bonds is called potential energy. It depends on the structure of an object or the position of matter in space. Raising a kettlebell changes its location and increases its potential energy. A stretched rubber band also stores potential energy, which can later change into kinetic energy. Chemical bonds between atoms hold another form of stored energy called chemical energy. These bonds involve attractive forces, and that energy can change into other forms during a...

free energy

Gibbs Free Energy in Chemical Reactions

Gibbs free energy is a measure of useful energy that can be taken from a chemical reaction to do work. It is written as G and named for scientist Gibbs, who discovered it. This energy is what remains after entropy is considered. A reaction can either take in energy or release it. Reactions that absorb energy are called endergonic reactions. Reactions that release energy are called exergonic reactions. The direction of energy flow helps show which type of reaction is happening. Plants carry...

activation energy

How Catalysts Lower Reaction Barriers

Activation energy is the minimum energy a chemical reaction needs to keep going. When the activation energy is higher, the reaction usually happens more slowly. Adding heat can speed the reaction because molecules move faster and collide more often. As reactants collide, bonds break and the reaction moves through an uphill phase. That step creates the transition state, which is an unstable, high-energy state of the reactants. After that, new bonds form, products appear, and free energy is...

hydrolysis of atp

ATP Breakdown and Energy Release

ATP breakdown releases energy for cell work. Adenosine triphosphate, or ATP, can lose one or two phosphate groups when water is added. This hydrolysis reaction is exergonic, which means it releases energy that the cell can use. When one phosphate group is removed, ATP becomes ADP, or adenosine diphosphate. Inorganic phosphate is also released. ADP can then be hydrolyzed again to form AMP, or adenosine monophosphate, after a second phosphate group is removed. ATP has a clear structure. It is...

phosphorylation

Phosphorylation and Protein Control

Phosphorylation helps control how proteins work in cells. It is the addition or removal of phosphate groups, and it is the most common chemical change that regulates cellular processes. These changes can alter a protein’s structure, activity, stability, location inside the cell, and interactions with other proteins. During phosphorylation, protein kinases move the terminal phosphate group from ATP to a specific amino acid side chain on a target protein. The amino acids most often...

induced-fit model

How Enzymes Adjust to Their Substrates

Enzymes speed up many chemical reactions in cells. They are biological catalysts, so they increase reaction speed without being consumed or permanently changed. They do this by lowering the activation energy needed to turn reactants into products. Enzymes are proteins that usually work by binding to a substrate, which is the reactant molecule they act on. They show substrate specificity, meaning they bind only certain substrates. This specificity depends mainly on the shape and chemical...

enzyme kinetics

Substrate Effects on Enzyme Rates

Enzyme kinetics examines how enzymes change the rate of a reaction. Enzymes speed reactions by lowering the activation energy of the reactants. The reaction rate is the speed at which an enzyme turns reactants into products, and it can be affected by several factors, including the number of available reactants. Scientists often study enzyme kinetics in a test tube with a fixed amount of enzyme. When more substrate, or reactant, is added, the reaction rate increases because the enzyme can make...

enzyme inhibition

Competitive vs Noncompetitive Inhibitors

Enzyme inhibitors are molecules that reduce enzyme activity by binding to enzymes. Cells use these inhibitors to help regulate normal enzyme function. Drugs and toxins can also block enzymes and change how they work. Some inhibitors bind at the active site, which is the part of the enzyme where the substrate normally fits. Competitive inhibitors do this by occupying the active site and preventing the substrate from binding. If the substrate concentration becomes high enough, it can outcompete...

feedback inhibition

How Cells Control Product Buildup

Cells use enzymes to run biochemical reactions and make the products they need. These reactions are happening constantly, and enzymes speed them up so they happen fast enough to matter. Enzyme activity also has to be regulated. Cells need the right amounts of starting materials, intermediate metabolites, and final products. If these substances build up too much or drop too low, the cell can be harmed. That is why cells use control systems to keep metabolic levels balanced. One important...

allosteric regulation

Allosteric Control of Enzyme Speed

Allosteric control changes enzyme speed when a molecule binds to a site other than the active site. That alternate binding spot is called an allosteric site. An enzyme can have more than one allosteric site. This type of control can raise or lower enzyme activity. Many enzymes with allosteric control are metabolic enzymes. They help with the breakdown or the building of specific molecules in cells. In allosteric inhibition, the effector molecule causes a shape change that lowers the enzyme's...

cofactors and coenzymes

Enzyme helpers are needed for many enzymes to work properly. These helpers fall into two groups: cofactors and coenzymes. Cofactors are metallic ions, while coenzymes are non-protein organic molecules. Both can be tightly bound to an enzyme or attach only when the substrate binds. Cofactors are common in mature proteins, appearing in about 30% of them. They are often added as the enzyme folds and help with catalytic activity. Magnesium is one important cofactor, and it is needed by more than...

key terms and concepts

Learn how cofactors and coenzymes help enzymes work, from magnesium in DNA polymerase to biotin and other vitamin-based helpers.

Enzyme Helpers: Metals, Vitamins, and More | JoVE K12

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Enzyme Helpers: Metals, Vitamins, and More

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