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

- [Instructor] Dentro de una celda,

diferentes condiciones ambientales

tales como la concentración de sustrato,

puede influir mucho en la tasa

en que las enzimas catalizan
las reacciones químicas.

Este proceso, llamado cinética enzimática,

se puede representar gráficamente

con la velocidad de reacción en el eje Y

y la condicion variable,

que es concentración de sustrato
en el ejemplo, en el eje X.

La velocidad de la
reacción es la velocidad

en la que se forma el producto,

y puede alcanzar una velocidad
máxima, conocida como "V max"

que alcanza su meseta cuando
todas las enzimas disponibles

se unen a sustratos.

Por lo tanto, la velocidad
de reacción es limitada

por la concentración de enzimas
disponibles para la unión.

Este gráfico también
puede revelar la velocidad

a la que aumenta la velocidad de reacción.

La variable se refleja con Km,

la concentración de sustrato
a la mitad de V max,

y representa la afinidad de la enzima

o la tendencia a unirse al sustrato.

Una enzima con un Km bajo
tiene una alta afinidad

porque alcanza su máxima
velocidad de reacción

a una baja concentración de sustrato.

Del mismo modo, un alto Km
corresponde a una baja afinidad

porque la enzima requiere
una mayor concentración

de sustrato para maximizar
su velocidad de reacción.

Johnson, Kenneth A. "Un siglo de análisis cinético de enzimas, 1913 a 2013". FEBS Letters 587, no. 17 (2 de septiembre de 2013): 2753–66. [<a href="https://doi.org/10.1016/j.febslet.2013.07.012">Fuente</a>]
Suárez, R. K., J. F. Staples, J. R. B. Lighton y T. G. West. "Relaciones entre las capacidades de flujo enzimático y las tasas de flujo metabólico: reacciones de no equilibrio en la glucólisis muscular". Actas de la Academia Nacional de Ciencias de los Estados Unidos de América 94, no. 13 (24 de junio de 1997): 7065–69. [<a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC21285/.">Fuente</a>]

la cinética de enzimas

Enzyme Kinetics

Las enzimas aceleran las reacciones al reducir la energía de activación de los reactivos. La velocidad a la que la enzima convierte los reactivos en productos se llama velocidad de reacción. Varios factores afectan la velocidad de reacción, incluida la cantidad de reactivos disponibles. La cinética enzimática es el estudio de cómo una enzima cambia la velocidad de una reacción. Los científicos suelen estudiar la cinética de las enzimas con una cantidad fija de enzima en el entorno controlado de un tubo de ensayo. Cuando se agrega más reactivo o sustrato a una cantidad fija de enzima, la velocidad de la reacción aumenta a medida que la enzima puede producir más producto. Como resultado, cuando la velocidad de reacción se representa gráficamente frente a la concentración de sustrato, el aumento del sustrato aumenta la velocidad de reacción. Sin embargo, una vez que todos los sitios activos de la enzima están ocupados, la velocidad de reacción se estabiliza. La concentración de sustrato a la que se alcanza la velocidad máxima de reacción se denomina Vmax. El número de moléculas de enzima presentes limita la Vmax. Si se aumenta la cantidad de enzima, la Vmax aumenta, pero agregar más sustrato no tiene ningún efecto. La gráfica de velocidad de reacción versus concentración de sustrato puede revelar otras características importantes de la cinética de una enzima. La concentración de sustrato a la que la velocidad de reacción está a la mitad de Vmax (½ Vmax) se llama constante de Michaelis (Km). Km es una representación de la afinidad entre una enzima y un sustrato. Las enzimas con una Km más baja requieren menos sustrato para alcanzar la Vmax, y por lo tanto, tienen una mayor afinidad por su sustrato. Curiosamente, para muchas enzimas, el valor de Km está muy cerca de la concentración celular del sustrato. Cerca de Km, ligeros cambios en la concentración del sustrato pueden afectar significativamente la velocidad de reacción, por lo que pequeños cambios en la disponibilidad del sustrato celular pueden afectar la función de una vía biológica completa. No todas las enzimas producen el gráfico de tasa de sustrato de forma hiperbólica conocido como cinética de Michaelis Menten. La cinética de Michaelis Menten supone que la enzima cataliza un único sustrato. Las enzimas que se regulan alostéricamente tienen múltiples sitios activos y tienden a producir un gráfico en forma de sigmoide cuando se representa la velocidad de reacción frente a la concentración del sustrato.

La cinética de enzimas

Las enzimas aceleran las reacciones al disminuir la energía de activación de los reactivos. La velocidad a la que la enzima convierte los reactivos en productos se denomina ...

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KEY TERMS AND CONCEPTS

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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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