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

Kinetyka enzymów bada szybkość reakcji katalizowanych enzymami. Tempo powtarzania eksperymentów przy różnych stężeniach substratów jest monitorowane poprzez pomiar stężenia zużytego substratu lub produktu powstałego w czasie.
Wyniki te można przedstawić na wykresie, aby pokazać, w jaki sposób stężenie substratu wpływa na szybkość lub szybkość reakcji.
Szybkość reakcji wzrasta liniowo wraz ze wzrostem ilości substratu przy niskich stężeniach, ale zaczyna się stabilizować przy wyższych stężeniach. Szybkość zbliża się do maksymalnej prędkości lub Vmax – szybkości, w której enzym jest całkowicie nasycony substratem.
Powinowactwo enzymatyczne mierzy, jak silnie lub słabo enzym wiąże swój substrat i jest określane ilościowo przez KM, stałą Michaelisa. Wartość KM jest równa stężeniu substratu, gdy szybkość wynosi 50% Vmax.
Małe KM oznacza, że enzym ma wysokie powinowactwo do substratu i odwrotnie. Enzym o większym KM wymaga wyższych stężeń substratu, aby zbliżyć się do maksymalnej prędkości w porównaniu z enzymem o niższym KM.

Johnson, Kenneth A. "Stulecie analizy kinetycznej enzymów, 1913 do 2013 roku." FEBS Letters 587, nr 17 (2 września 2013): 2753–66. [<a href="https://doi.org/10.1016/j.febslet.2013.07.012">Źródło</a>]
Suarez, R. K., J. F. Staples, J. R. B. Lighton i T. G. West. "Zależności między zdolnościami strumienia enzymatycznego a szybkością strumienia metabolicznego: reakcje nierównowagi w glikolizie mięśni". Proceedings of the National Academy of Sciences of the United States of America 94, nr 13 (24 czerwca 1997): 7065–69. [<a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC21285/.">Źródło</a>]

kinetyka enzymów

Enzyme Kinetics

Enzymy przyspieszają reakcje, obniżając energię aktywacji reagentów. Szybkość, z jaką enzym przekształca reagenty w produkty, nazywa się szybkością reakcji. Na szybkość reakcji wpływa kilka czynników, w tym liczba dostępnych reagentów. Kinetyka enzymu to badanie tego, jak enzym zmienia szybkość reakcji.

Naukowcy zazwyczaj badają kinetykę enzymów przy stałej ilości enzymu w kontrolowanym środowisku probówki. Kiedy do ustalonej ilości enzymu dodaje się więcej reagenta lub substratu, szybkość reakcji wzrasta, ponieważ enzym może wytworzyć więcej produktu. W rezultacie, gdy szybkość reakcji jest przedstawiana na wykresie w zależności od stężenia substratu, zwiększenie substratu zwiększa szybkość reakcji. Jednakże, gdy wszystkie miejsca aktywne enzymu zostaną zajęte, szybkość reakcji utrzymuje się na stałym poziomie. Stężenie substratu, przy którym osiągana jest maksymalna szybkość reakcji, nazywa się Vmax. Liczba obecnych cząsteczek enzymu ogranicza Vmax. Jeśli ilość enzymu zostanie zwiększona, Vmax wzrośnie, ale dodanie większej ilości substratu nie przyniesie efektu.

Wykres szybkości reakcji w zależności od stężenia substratu może ujawnić inne ważne cechy kinetyki enzymu. Stężenie substratu, przy którym szybkość reakcji jest w połowie drogi do Vmax (tj. ½ Vmax) nazywane jest stałą Michaelisa (Km). Km jest reprezentacją powinowactwa pomiędzy enzymem a substratem. Enzymy o niższym Km wymagają mniej substratu, aby osiągnąć Vmax i dlatego mają większe powinowactwo do swojego substratu. Co ciekawe, dla wielu enzymów wartość Km jest bardzo zbliżona do komórkowego stężenia substratu. W pobliżu Km niewielkie zmiany w stężeniu substratu mogą znacząco wpłynąć na szybkość reakcji, więc niewielkie zmiany w dostępności substratu komórkowego mogą mieć wpływ na funkcję całego szlaku biologicznego.

Nie wszystkie enzymy tworzą hiperboliczny wykres szybkości substratu, znany jako kinetyka Michaelisa Mentena. Kinetyka Michaelisa Mentena zakłada, że enzym katalizuje pojedynczy substrat. Enzymy regulowane allosterycznie mają wiele miejsc aktywnych i mają tendencję do tworzenia wykresu w kształcie esicy, gdy szybkość reakcji jest wykreślana w funkcji stężenia substratu.

Kinetyka enzymów

Enzymy przyspieszają reakcje poprzez obniżenie energii aktywacji reagentów. Prędkość, z jaką enzym przekształca reagenty w produkty, nazywana jest ...

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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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Substrate Effects on Enzyme Rates

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