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

Innerhalb einer Zelle können verschiedene Umweltbedingungen, wie zum Beispiel die Substratkonzentration, die Rate wesentlich beeinflussen, in der Enzyme chemische Reaktionen katalysieren.
 Dieser Vorgang, Enzymkinetik genannt, kann grafisch dargestellt werden, wobei die Reaktionsrate auf der y-Achse und die variierende Bedingung, in diesem Beispiel die Substratkonzentration, auf der x-Achse liegt.
 Die Reaktionsrate ist die Rate, zu der das Produkt geformt wird.
 Sie kann eine maximale Geschwindigkeit erreichen, V max genannt, die das Hoch erreicht, wenn alle verfügbaren Enzyme mit Substraten verbunden sind.
 Dadurch wird die Reaktionsrate durch die Konzentration der für eine Verbindung vorhandenen Enzyme eingeschränkt.
 Dieser Graph zeigt zudem die Geschwindigkeit, zu der die Reaktionsrate ansteigt.
 Die Variable wird durch Km reflektiert, die Substratkonzentration bei der Hälfe von V max, und stellt die Affinität oder Tendenz des Enzyms dar, sich mit dem Substrat zu verbinden.
 Ein Enzym mit einem niedrigen Km hat eine hohe Affinität, da es seine maximale Reaktionsrate bei einer niedrigen Substratkonzentration erreicht.
 Genauso entspricht ein hoher Km einer niedrigen Affinität, da das Enzym eine höhere Konzentration des Substrats braucht, um die Reaktionsrate zu maximieren.

Johnson, Kenneth A. "Ein Jahrhundert der kinetischen Enzymanalyse, 1913 bis 2013." FEBS Letters 587, Nr. 17 (2. September 2013): 2753–66. [<a href="https://doi.org/10.1016/j.febslet.2013.07.012">Quelltext</a>]
Suarez, R. K., J. F. Staples, J. R. B. Lighton und T. G. West. "Beziehungen zwischen enzymatischen Flusskapazitäten und metabolischen Flussraten: Nichtgleichgewichtsreaktionen bei der Muskelglykolyse." Verfahren der Nationalen Akademie der Wissenschaften der Vereinigten Staaten von Amerika 94, Nr. 13 (24. Juni 1997): 7065–69. [<a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC21285/.">Quelle</a>]

enzymkinetik

Enzyme Kinetics

Enzyme beschleunigen die Reaktionszeit, indem sie die Aktivierungsenergie der Edukte senken. Man bezeichnet die Geschwindigkeit, mit der ein Enzym Edukte in Produkte umwandelt, als Reaktionsgeschwindigkeit. Mehrere Faktoren beeinflussen die Reaktionsgeschwindigkeit, wie auch die Menge der verfügbaren Edukte. Die Enzymkinetik untersucht wie ein Enzym die Reaktionsgeschwindigkeit beeinflusst.
 
 Wissenschaftler untersuchen die Enzymkinetik eines Enzyms normalerweise mit einer bestimmten Enzymmenge in der kontrollierten Umgebung eines Reagenzglases. Wenn einer bestimmten Enzymmenge mehr Edukte oder Substrate hinzugefügt werden, erhöht sich die Reaktionsgeschwindigkeit, während das Enzym mehr Produkte herstellt. Wenn die Reaktionsgeschwindigkeit und die Substratkonzentration in einem Graphen dargestellt werden, zeigt sich das die Erhöhung des Substrats die Reaktionsgeschwindigkeit erhöht. Wenn jedoch alle aktiven Zentren des Enzyms besetzt sind, erreicht die Reaktionsgeschwindigkeit ein Plateau. Die Substratkonzentration, bei der die maximale Reaktionsgeschwindigkeit erreicht wird, wird als Vmax bezeichnet. Die Anzahl der vorhandenen Enzymmoleküle begrenzt Vmax. Wenn die Menge des Enzyms erhöht wird, steigt Vmax, während die Zugabe von mehr Substrat keine Wirkung hat.
 
 Die grafische Darstellung der Reaktionsgeschwindigkeit gegenüber der Substratkonzentration kann weitere wichtige Eigenschaften der Enzymkinetik zeigen. Die Substratkonzentration, bei der die Reaktionsgeschwindigkeit die Hälfte des Vmax (d.h. 1/2 Vmax) ist, wird als Michaeliskonstante (Km) bezeichnet. Km beschreibt die Affinität zwischen einem Enzym und dem Substrat. Enzyme mit einem kleinerem Km benötigen weniger Substrat, um Vmax zu erreichen, und haben daher eine höhere Affinität für das Substrat. Interessanterweise ist der Wert des Kms bei vielen Enzymen ähnlich der zellulären Konzentration des Substrats. Bei Werten nahe des Kms können kleine Änderungen in der Substratkonzentration die Reaktionsgeschwindigkeit erheblich beeinflussen, so dass kleine Veränderungen der zellulären Substratverfügbarkeit die Funktion eines gesamten biologischen Weges beeinflussen können.
 
 Nicht alle Enzyme erzeugen die hyperbole Kurve des Substrat-Reaktionsgeschwindigkeits-Graphen, welcher als Michaelis-Menten-Theorie bekannt ist. Die Michaelis-Menten-Theorie geht davon aus, dass das Enzym ein einzelnes Substrat katalysiert. Enzyme, die allosterisch reguliert werden, haben mehrere aktive Zentren und neigen dazu, eine sigmoide Kurve zu bilden, wenn die Reaktionsgeschwindigkeit gegen die Substratkonzentration aufgetragen wird.

Enzymkinetik

Enzyme beschleunigen Reaktionen, indem sie die Aktivierungsenergie der Reaktanten senken. Die Geschwindigkeit, mit der das Enzym Reaktanten in Produkte umwandelt, wird als ...

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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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