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

Внутри клетки, различные условия окружающей среды, такие как концентрация субстрата, могут оказывать значительное влияние на скорость, с которой ферменты катализируют химические реакции. Этот процесс, называемый кинетикой фермента, может быть представлен графически со скоростью реакции на оси y, и изменяющимся состоянием, концентрацией субстрата в в данном примере, отложенной по оси x. Скорость реакции это скорость, с которой образуется продукт, и может достигать максимальной скорости, известной как Vmax, которая выходит на плато, когда все доступные ферменты связаны с субстратами.Поэтому скорость реакции ограничена концентрацией ферментов, доступных для связывания. На этом графике также отображается величина, при которой темпы реакции увеличиваются. Переменная, обозначенная Km концентрация субстрата при половине величины Vmax, и представляет сродство фермента, или склонность к привязке к субстрату.Фермент с низкой Км имеет высокое сродство, потому что он достигает своей максимальной скорости реакции при низкой концентрации субстрата. Точно так же, высокая Кm соответствует низкому сродству, так как фермент требует более высокую концентрацию субстрата для максимального увеличения скорости реакции.

Джонсон, Кеннет А. "Столетие ферментного кинетического анализа, с 1913 по 2013 год." FEBS Letters 587, No17 (2 сентября 2013 г.): 2753–66. [<a href="https://doi.org/10.1016/j.febslet.2013.07.012">исходник</a>]
Суарес, Р. К., Д. Ф. Стейплс, Дж. Р. Б. Лайтон и Т. Г. Уэст. "Взаимосвязь между ферментативными возможностями потока и скоростью метаболического потока: неравновесные реакции в мышечном гликолизе." Труды Национальной академии наук Соединенных Штатов Америки 94, No13 (24 июня 1997): 7065–69. [<a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC21285/.">Источник</a>]

Ингибирование ферментов

Enzyme Kinetics

Ферменты ускоряют реакции за счет снижения энергии активации реагентов. Скорость, с которой фермент превращает реагенты в продукты, называется скоростью реакции. На скорость реакции влияют несколько факторов, включая количество доступных реагентов. Кинетика ферментов - это изучение того, как фермент изменяет скорость реакции. 

 Ученые обычно изучают кинетику ферментов с фиксированным количеством фермента в контролируемой среде пробирки. Когда к фиксированному количеству фермента добавляется больше реагента или субстрата, скорость реакции увеличивается, поскольку фермент может производить больше продукта. В результате, когда скорость реакции отображается на графике в зависимости от концентрации субстрата, увеличение субстрата увеличивает скорость реакции. Однако, как только все активные центры фермента заняты, скорость реакции выходит на плато. Концентрация субстрата, при которой достигается максимальная скорость реакции, называется V max . Количество присутствующих молекул фермента ограничивает V max . Если количество фермента увеличивается, V max увеличивается, но добавление большего количества субстрата не имеет никакого эффекта. 

 График зависимости скорости реакции от концентрации субстрата может выявить другие важные характеристики кинетики фермента. Концентрация субстрата, при которой скорость реакции составляет половину V max (т.е. & frac12; V max ), называется константой Михаэлиса (K m ). K m - это представление сродства между ферментом и субстратом. Ферменты с более низким K m требуют меньше субстрата для достижения V max и, следовательно, имеют более высокое сродство к своему субстрату. Интересно, что для многих ферментов значение K m очень близко к клеточной концентрации субстрата. Вблизи K m небольшие изменения концентрации субстрата могут значительно повлиять на скорость реакции, поэтому небольшие изменения в доступности клеточного субстрата могут повлиять на функцию всего биологического пути. 

 Не все ферменты создают график содержания субстрата в гиперболической форме, известный как кинетика Михаэлиса Ментен. Кинетика Michaelis Menten предполагает, что фермент катализирует единственный субстрат. Ферменты, которые регулируются аллостерически, имеют несколько активных центров и имеют тенденцию давать сигмовидный график, когда скорость реакции отображается в зависимости от концентрации субстрата.

Ферменты ускоряют реакции, снижая энергию активации реагентов. Скорость, с которой фермент превращает реагенты в продукты, называется ...

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ОСНОВНЫЕ ТЕРМИНЫ И ПОНЯТИЯ

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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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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