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

- [Instructeur] Binnen een cel kunnen verschillende omgevingscondities, zoals substraatconcentratie, de snelheid waarmee enzymen chemische reacties katalyseren sterk beïnvloeden. Dit proces genaamd enzyme kinetiek kan grafisch worden weergegeven met de reactiesnelheid op de Y-as en de wisselende toestand, substraatconcentratie in dit voorbeeld, op de X-as. De snelheid van de reactie is de snelheid waarmee het product wordt gevormd een maximale snelheid bereikt die bekend staat als Vmax, plateauing wanneer alle beschikbare enzymen aan substraten gebonden zijn.

Daarom wordt de reactiesnelheid beperkt door de concentratie van de voor binding beschikbare enzymen. Deze grafiek kan ook de snelheid weergeven waarmee de reactiesnelheid toeneemt. De variabele wordt gereflecteerd door Km, de substraatconcentratie op de helft van Vmax en vertegenwoordigt de affiniteit van het enzym voor, of de neiging om zich aan het substraat te binden.

Een enzym met een lage Km heeft een hoge affiniteit, omdat het bij een lage substraatconcentratie zijn maximale reactiesnelheid bereikt. Ook komt een hoge Km overeen met een lage affiniteit, omdat het enzym een hogere concentratie substraat nodig heeft om de reactiesnelheid te maximaliseren.

enzymkinetiek

Enzyme Kinetics

Enzymen versnellen reacties door de activeringsenergie van de reactanten te verlagen. De snelheid waarmee het enzym reactanten in producten omzet, wordt de reactiesnelheid genoemd. Verschillende factoren beïnvloeden de reactiesnelheid, inclusief het aantal beschikbare reactanten. Enzymkinetiek is de studie van hoe een enzym de snelheid van een reactie verandert.

Wetenschappers bestuderen de kinetiek van enzymen doorgaans met een vaste hoeveelheid enzym in de gecontroleerde omgeving van een reageerbuis.Wanneer meer reactant of substraat aan een vaste hoeveelheid enzym wordt toegevoegd, neemt de reactiesnelheid toe naarmate het enzym meer product kan maken. Als resultaat hiervan, wanneer de reactiesnelheid wordt uitgezet tegen de substraatconcentratie, verhoogt het verhogen van het substraat de reactiesnelheid. Zodra echter alle actieve plaatsen van het enzym bezet zijn, bereikt de reactiesnelheid een plateau. De substraatconcentratie waarbij de maximale reactiesnelheid wordt bereikt, wordt Vmax genoemd. Het aantal aanwezige enzymmoleculen beperkt Vmax. Als de hoeveelheid enzym wordt verhoogd, neemt de Vmax toe, maar het toevoegen van meer substraat heeft geen effect.

De grafiek van de reactiesnelheid versus de substraatconcentratie kan andere belangrijke kenmerken van de kinetiek van een enzym onthullen. De substraatconcentratie waarbij de reactiesnelheid halverwege Vmax ligt (d.w.z. ½ Vmax) wordt de Michaelis-constante (Kmax) genoemd. Km is een weergave van de affiniteit tussen een enzym en een substraat. Enzymen met een lagere Kmax hebben minder substraat nodig om Vmax te bereiken en hebben daarom een hogere affiniteit voor hun substraat. Interessant is dat voor veel enzymen de waarde van Kmax zeer dicht bij de cellulaire concentratie van het substraat ligt. In de buurt van Kmax kunnen kleine veranderingen in de substraatconcentratie de reactiesnelheid aanzienlijk beïnvloeden, dus kleine veranderingen in de beschikbaarheid van cellulair substraat kunnen de functie van een volledig biologisch pad beïnvloeden.

Niet alle enzymen produceren de hyperbolisch gevormde substraatsnelheidsgrafiek die bekend staat als de Michaelis Menten-kinetiek. De kinetiek van Michaelis Menten gaat ervan uit dat het enzym een enkel substraat katalyseert. Enzymen die allosterisch worden gereguleerd, hebben meerdere actieve plaatsen en hebben de neiging een sigmoïdvormige grafiek te produceren wanneer de reactiesnelheid wordt uitgezet tegen de substraatconcentratie.

Enzymkinetiek

Enzymes speed up reactions by lowering the activation energy of the reactants. The speed at which the enzyme turns reactants into products is called the ...

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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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