Name: substrate effects on enzyme rates
Uploaded: 2019-08-01T09:12:17.000Z
Duration: 1 min 19 s
Channel: JoVE

세포 안에서 기질 농도와 같은 환경 조건은세포 안에서 기질 농도와 같은 환경 조건은세포 안에서 기질 농도와 같은 환경 조건은효소가 화학 반응을 촉진하는 속도에 많은 영향을 끼칠 수 있습니다.효소가 화학 반응을 촉진하는 속도에 많은 영향을 끼칠 수 있습니다.효소 운동이라 불리는 이 과정은,그래프로도 보여질 수 있습니다.y축인 반응 속도와이 예에서는 기질 농도인, x축인 변수 조건을 통해서 말이죠.이 예에서는 기질 농도인, x축인 변수 조건을 통해서 말이죠.반응 속도는 생산물이 형성되는 속도이며,반응 속도는 생산물이 형성되는 속도이며,V max라 불리는 최고 속도에 다다를 수 있고이용 가능한 효소가 모두 기질에 결합할 때 안정 상태를 유지할 수 있습니다.이용 가능한 효소가 모두 기질에 결합할 때 안정 상태를 유지할 수 있습니다.그러므로 반응 속도는결합에 가능한 효소 농도에 따라 제한됩니다.이 그래프로 반응 속도가 어느 속도로 증가하는지도 알 수 있습니다.이 그래프로 반응 속도가 어느 속도로 증가하는지도 알 수 있습니다.변수는 Km,V max 절반의 기질 농도로 표현되며효소의 친화력,기질에 결합하려는 경향이 보여줍니다.낮은 Km을 가진 효소는 높은 친밀감을 갖고 있으며이는 최고 반응 속도를낮은 기질 농도에서 다다를 수 있기 때문입니다.유사하게, 높은 Km은 낮은 친화력과 일치하며이는 효소가 최대의 반응 속도를 내기 위해서는더 높은 기질 농도가 필요하기 때문입니다.

Johnson, Kenneth A. "A Century of Enzyme Kinetic Analysis, 1913 to 2013." FEBS Letters 587, no. 17 (2013년 9월 2일): 2753–66. [<a href="https://doi.org/10.1016/j.febslet.2013.07.012">출처</a>]
Suarez, R. K., J. F. Staples, J. R. B. Lighton, and T. G. West. "Relationships between Enzymatic Flux Capacities and Metabolic Flux Rates: Nonequilibrium Reactions in Muscle Glycolysis(효소 플럭스 용량과 대사 플럭스 속도 간의 관계: 근육 해당작용에서의 비평형 반응)", Proceedings of the National Academy of Sciences of the United States of America 94, no. 13 (June 24, 1997): 7065–69. [<a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC21285/.">출처</a>]

효소 반응속도론

Enzyme Kinetics

효소(enzyme)는 반응물(reactant)의 활성화 에너지(activation energy)를 낮추어 반응을 가속합니다. 효소가 반응물을 생성물(product)로 바꾸는 속도를 반응속도(reaction rate)라고 합니다. 사용 가능한 반응물 수를 포함하여 반응속도에 영향을 미치는 요인은 여러 가지가 있습니다. 효소 반응속도론(enzyme kinetics)은 효소가 반응속도를 어떻게 변화시키는지에 대한 연구입니다.
 
 과학자들은 시험관의 통제된 환경에 놓인 일정한 양의 효소를 가지고 효소 반응속도론을 연구합니다. 정해진 양의 효소에 더 많은 반응물, 즉 기질(substrate)이 첨가되면, 효소가 더 많은 생성물을 만들 수 있기 때문에 반응속도가 증가합니다. 결과적으로 기질 농도에 대한 반응속도를 그래프로 나타낼 때, 기질을 증가시키면 반응속도가 증가합니다. 하지만, 일단 효소의 모든 활성부위가 점령되면, 반응속도는 평형에 도달합니다. 최대 반응속도에 도달하는 기질의 농도를 Vmax라고 합니다. 현재 효소 분자의 수는 Vmax를 제한합니다. 효소의 양이 증가하면 Vmax는 증가하지만, 더 많은 기질을 첨가하는 것은 효과가 없습니다.
 
 반응속도 대 기질 농도의 그래프는 효소 반응속도론의 다른 중요한 특징들을 나타낼 수 있습니다. 반응속도가 Vmax(즉, ½ Vmax)의 절반에 해당하는 기질 농도를 미카엘리스 상수(Michaelis constant, 줄여서 Km)라고 합니다. Km은 효소와 기질 사이의 친화력(affinity)을 나타냅니다. Km이 낮은 효소는 Vmax에 도달하는 데 필요한 기질이 적기 때문에 기질에 대한 친화력이 높습니다. 많은 효소의 경우, Km의 값은 기질의 세포 농도에 매우 가깝습니다. Km 근처에서는 기질 농도의 약간의 변화가 반응속도에 상당한 영향을 미칠 수 있으므로 세포 기질 가용성의 작은 변화가 생물학적 경로의 전반적인 기능에 영향을 미칠 수 있습니다.
 
 모든 효소가 미카엘리스-멘텐 반응속도식(Michaelis Menten kinetics)으로 알려진 쌍곡선(hyperbolic) 모양의 기질 속도 그래프를 생성하는 것은 아닙니다. 미카엘리스-멘텐 반응속도식은 효소가 단일 기질을 촉매한다고 가정합니다. 다른자리입체성(allostery)으로 조절되는 효소는 여러 활성부위(active site)가 있으며, 반응속도를 기질 농도와 비교할 때 S자 모양의 그래프를 생성하는 경향이 있습니다.

효소는 반응물의 활성화 에너지를 낮춰 반응 속도를 높입니다. 효소가 반응물을 생성물로 바꾸는 속도를 ...

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주요 용어 및 개념

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 more product. If the reaction rate is graphed against substrate concentration, the curve rises as substrate increases.

The rate does not keep rising forever. Once all of the enzyme's active sites are occupied, the reaction rate levels off. The substrate concentration at which the maximum rate is reached is called V max. V max is limited by the number of enzyme molecules present. If more enzyme is added, V max increases, but more substrate alone has no further effect.

A rate-versus-substrate graph can also show other features of enzyme behavior. The substrate concentration at which the reaction rate is halfway to V max is called the Michaelis constant, or K m. K m shows the affinity between an enzyme and its substrate. A lower K m means less substrate is needed to reach V max, so the enzyme has a higher affinity.

For many enzymes, K m is close to the substrate concentration in cells. Near K m, even small changes in substrate concentration can strongly affect the reaction rate. That means small shifts in cellular substrate availability can influence the activity of an entire biological pathway.

Not all enzymes follow Michaelis Menten kinetics. This model assumes that an enzyme acts on a single substrate. Enzymes regulated allosterically have multiple active sites and usually produce a sigmoid-shaped graph instead of a hyperbolic one when reaction rate is plotted against substrate concentration.

Substrate Effects on Enzyme Rates

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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...

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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

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

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feedback inhibition

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Allosteric Control of Enzyme Speed

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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...

key terms and concepts

Learn how substrate concentration changes enzyme reaction rate, and how V max, K m, and allosteric enzymes shape enzyme kinetics in high school biology.

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Substrate Effects on Enzyme Rates

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