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

- [Istruttore] All'interno di una cellula

diverse condizioni ambientali,

come la concentrazione del substrato,

possono influenzare
notevolmente la velocità

con cui gli enzimi catalizzano
le reazioni chimiche.

Questo processo, chiamato
cinetica enzimatica,

può essere rappresentato graficamente

con la velocità di reazione sull'asse y

e la condizione variabile,

concentrazione del substrato
in questo esempio, sull'asse x.

La velocità della reazione è la velocità

alla quale il prodotto è formato

e può raggiungere una velocità
massima, nota come V max,

che si estende quando tutti
gli enzimi disponibili

sono legati ai substrati.

Pertanto la velocità
di reazione è limitata

dalla concentrazione di enzimi
disponibili per il legame.

Questo grafico può anche
rivelare la velocità

con cui aumenta la velocità di reazione.

La variabile viene riflessa da "Km",

la concentrazione del
substrato a metà della V max

e rappresenta l'affinità dell'enzima

o la tendenza a legarsi al substrato.

Un enzima con un Km
basso ha un'alta affinità

perché raggiunge la massima
velocità di reazione

a una bassa concentrazione di substrato.

In modo simile, un numero di km elevato

corrisponde a una bassa affinità

perché l'enzima richiede
una maggiore concentrazione

di substrato per massimizzare
la sua velocità di reazione.

Johnson, Kenneth A. "Un secolo di analisi cinetica enzimatica, dal 1913 al 2013". Lettere FEBS 587, n. 17 (2 settembre 2013): 2753–66. [<a href="https://doi.org/10.1016/j.febslet.2013.07.012">Fonte</a>]
Suarez, R. K., J. F. Staples, J. R. B. Lighton e T. G. West. "Relazioni tra capacità di flusso enzimatico e tassi di flusso metabolico: reazioni di non equilibrio nella glicolisi muscolare." Atti dell'Accademia Nazionale delle Scienze degli Stati Uniti d'America 94, n. 13 (24 giugno 1997): 7065-69. [<a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC21285/.">Sorgente</a>]

cinetiche enzimatiche

Enzyme Kinetics

Gli enzimi accelerano le reazioni abbassando l'energia di attivazione dei reagenti. La velocità alla quale l'enzima trasforma i reagenti in prodotti è chiamata velocità di reazione. Diversi fattori influenzano il tasso di reazione, compreso il numero di reagenti disponibili. La cinetica enzimatica è lo studio di come un enzima cambia il tasso di una reazione.

Gli scienziati in genere studiano la cinetica enzimatica con una quantità fissa di enzimi nell'ambiente controllato di una provetta. Quando più reattore, o substrato, viene aggiunto a una quantità fissa di enzima, il tasso di reazione aumenta come l'enzima può fare più prodotto. Di conseguenza, quando il tasso di reazione è rappresentato graficamente rispetto alla concentrazione di substrato, aumentando il substrato aumenta il tasso di reazione. Tuttavia, una volta occupati tutti i siti attivi dell'enzima, il tasso di reazione altipiani. La concentrazione di substrato al quale viene raggiunto il tasso massimo di reazione è chiamata Vmax. Il numero di molecole enzimatiche presenti limita Vmax. Se la quantità di enzima è aumentata, Vmax aumenta, ma l'aggiunta di più substrato non ha alcun effetto.

Il grafico del tasso di reazione rispetto alla concentrazione del substrato può rivelare altre importanti caratteristiche della cinetica di un enzima. La concentrazione di substrato alla quale la velocità di reazione è a metà del Vmax (cioè, 1/2 Vmax) è chiamata costante di Michaelis (Km). Km è una rappresentazione dell'affinità tra un enzima e un substrato. Gli enzimi con un Km inferiore richiedono meno substrato per raggiungere Vmax e quindi hanno una maggiore affinità per il loro substrato. È interessante notare che, per molti enzimi, il valore di Km è molto vicino alla concentrazione cellulare del substrato. Vicino a Km, lievi cambiamenti nella concentrazione di substrato possono avere un impatto significativo sul tasso di reazione, quindi piccoli cambiamenti nella disponibilità di substrato cellulare possono influenzare la funzione di un intero percorso biologico.

Non tutti gli enzimi producono il grafico a forma di substrato iperbolico noto come cinetica Michaelis Menten. La cinetica Michaelis Menten presuppone che l'enzima catalizzi un singolo substrato. Gli enzimi regolati all'origine hanno più siti attivi e tendono a produrre un grafico a forma di sigmoide quando il tasso di reazione viene tracciato rispetto alla concentrazione di substrato.

Cinetiche Enzimatiche

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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