Name: diffusion-controlled enzymes and reaction speed
Uploaded: 2023-04-30T10:09:49.000Z
Duration: 1 min 7 s
Channel: JoVE

K12 Standards

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North Carolina K-12 Science Standard Course of Study

9-12

Biology

from-molecules-to-organisms-structures-and-processes

From Molecules to Organisms- Structures and Processes

LS.Bio.1.2

Catalytically Perfect Enzymes

Les enzymes catalytiquement parfaites ont l’efficacité catalytique maximale avec des nombres de renouvellement élevés, kcat, et de fortes affinités pour leurs substrats, KM. 
 
Le rapport kcat à KM mesure l’efficacité catalytique. Pour les enzymes catalytiquement parfaites, cette valeur varie de 108 à 109 par substrat molaire et par seconde. 
 
La diffusion du substrat est le mouvement constant des molécules du substrat causé par le mouvement moléculaire. Les substrats doivent diffuser au sein de la cellule pour interagir avec leurs enzymes. 
 
Les vitesses de réaction des enzymes catalytiquement parfaites ne sont limitées que par la vitesse de diffusion du substrat ou de libération du produit à partir du site actif. Certaines enzymes ont atteint la perfection catalytique grâce à des forces électrostatiques qui attirent et guident les substrats dans leur site actif. 
 
Dans les enzymes catalytiquement parfaites, chaque collision enzyme-substrat produit un intermédiaire qui se transforme rapidement en produits.

<ol>
	<li>Ahern, K. et Rajagopal, I. (2021, 6 mars). Des enzymes parfaites. Université d’État de l’Oregon. https://bio.libretexts.org/@go/page/3036.</li>
	<li>Petterson, G. (1992). Optimisation évolutive de l’efficacité catalytique des enzymes. Revue européenne de biochimie, 206(1), 289-295.</li>
	<li>Bar-Even, A., Milo, R., Noor, E. et Tawfik, D. S. (2015). L’enzyme moyennement efficace : rencontres futiles et mollesse enzymatique. Biochimie, 54(32), 4969-4977.</li>
</ol>

les enzymes catalytiquement parfaites

La théorie des enzymes catalytiquement parfaites a été proposée pour la première fois par W.J. Albery et J.R. Knowles en 1976. Ces enzymes catalysent des réactions biochimiques à grande vitesse. Leurs valeurs d'efficacité catalytique vont de 108 à 109 M-1s-1. Ces enzymes sont également appelées « contrôlées par diffusion » car la seule étape limitante de la catalyse est celle de la diffusion du substrat dans le site actif. Des exemples inclueraient la triose phosphate isomérase, la fumarase et le superoxyde dismutase.

La plupart des enzymes atteignent la perfection catalytique grâce aux groupes chargés présents à leur surface qui orientent et dirigent le substrat vers le site actif. D’autres enzymes ont une disposition spécifique de leurs sites actifs, contribuant ainsi à la “perfection catalytique”. Penchons-nous un peu sur des enzymes telles que  le superoxyde dismutase,et  les ions métalliques (tels que le cuivre et le zinc). A proximité du site actif, des acides aminés chargés tels que l'arginine accélèrent la conversion de l'anion superoxyde en oxygène et peroxyde d'hydrogène. Les mutations aléatoires des enzymes favorisent de telles interactions avec leurs substrats, et les enzymes les plus efficaces parviennent à résister au fil du temps.

Des enzymes parfaites catalysent non seulement des réactions très efficaces, mais peuvent également aider à protéger les cellules contre les intermédiaires de réaction, nocifs. A titre d’exemple, la triose phosphate isomérase (TPI) est une enzyme de la voie glycolytique qui catalyse l'interconversion du dihydroxyacétone phosphate (DHAP) et du glycéraldéhyde 3-phosphate (G3P). La lente conversion du DHAP en G3P forme un intermédiaire énediol qui finit par se décomposer en un composé toxique. Le TPI étant une enzyme catalytiquement parfaite accélère la réaction et transforme rapidement l’intermédiaire en produit, évitant ainsi les composés indésirables. Jusqu’à l’heure actuelle, très peu d’enzymes sont connues être catalytiquement parfaites. La plupart sont moyennement efficaces.

Les enzymes catalytiquement parfaites

La théorie des enzymes catalytiquement parfaites a été proposée pour la première fois par W.J. Albery et J. R. Knowles en 1976. Ces enzymes catalysent des réactions biochimiques au niveau ...

Education

Enseignement

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Cell Biology

Biologie cellulaire

Unit 1

Unité 1

Energy and Catalysis

Énergie et catalyse

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

diffusion-controlled enzymes and reaction speed

Catalytically perfect enzymes are enzymes that speed up biochemical reactions at very high rates. The idea was first proposed by W. J. Albery and J. R. Knowles in 1976. These enzymes have catalytic efficiency values of about 10^8 to 10^9 M^-1 s^-1 and are also called diffusion-controlled enzymes because diffusion of the substrate into the active site is the only rate-limiting step.

Examples of catalytically perfect enzymes include triose phosphate isomerase, fumarase, and superoxide dismutase. In many cases, charged groups on the enzyme surface help orient and steer the substrate into the active site. Some enzymes also depend on a specific active site arrangement, which supports this very fast catalysis.

Superoxide dismutase shows how the active site can increase reaction speed. In this enzyme, metal ions such as copper and zinc work with charged amino acids like arginine near the active site. Together, they speed the conversion of superoxide anion into oxygen and hydrogen peroxide.

Catalytic perfection can also arise through natural selection. Random mutations may favor enzyme-substrate interactions, and enzymes with higher efficiency can be selected over time. Even so, only a few enzymes have evolved to this level, and most enzymes are only moderately efficient.

These enzymes can also protect cells from harmful reaction intermediates. Triose phosphate isomerase, or TPI, works in the glycolytic pathway and converts dihydroxyacetone phosphate, or DHAP, into glyceraldehyde 3-phosphate, or G3P. If DHAP changes too slowly, it forms an enediol intermediate that can break down into a toxic compound. Because TPI is catalytically perfect, it rapidly drives the reaction forward and helps prevent unwanted products.

Diffusion-Controlled Enzymes and Reaction Speed

diffusion-controlled-enzymes-reaction-speed

the first law of thermodynamics

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catalytically perfect enzymes

Catalytically perfect enzymes are enzymes that speed up biochemical reactions at very high rates. The idea was first proposed by W. J. Albery and J. R. Knowles in 1976. These enzymes have catalytic efficiency values of about 10^8 to 10^9 M^-1 s^-1 and are also called diffusion-controlled enzymes because diffusion of the substrate into the active site is the only rate-limiting step. Examples of catalytically perfect enzymes include triose phosphate isomerase, fumarase, and superoxide dismutase.

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key terms and concepts

Learn how catalytically perfect enzymes work, why diffusion can limit their speed, and how examples like TPI and superoxide dismutase protect cells.

Diffusion-Controlled Enzymes and Reaction Speed | JoVE K12

cell biology

JoVE Core Biologie cellulaire illustre les processus cellulaires complexes dans des leçons vidéos complètes mais faciles à comprendre. Cette collection se concentre sur les composants et fonctions essentiels de la cellule ; cela inclut les organelles et les membranes ainsi que le transport et le métabolisme énergétique cellulaire. Elle est complétée par nos vidéos de scientifiques à l'action qui démontrent l'application de la biologie cellulaire dans des expériences concrètes.

Virginia  Standards of Learning

HIgh School

BIO.2

BIO.2.c

Chemistry

CH.7

CH.7.f

Florida Department of Education

High School

Life Science

SC.912.L.18

SC.912.L.18.4

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Diffusion-Controlled Enzymes and Reaction Speed

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