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

Gli enzimi cataliticamente perfetti hanno la massima efficienza catalitica con alti numeri di turnover, kcat, e forti affinità per i loro substrati, KM. 
 
Il rapporto tra kcat e KM misura l'efficienza catalitica. Per enzimi cataliticamente perfetti, questo valore varia da 108 a 109 per substrato molare al secondo. 
 
La diffusione del substrato è il movimento costante delle molecole del substrato causato dal movimento molecolare. I substrati devono diffondersi all'interno della cellula per interagire con i loro enzimi. 
 
Le velocità di reazione degli enzimi cataliticamente perfetti sono limitate solo dalla velocità di diffusione del substrato o di rilascio del prodotto dal sito attivo. Alcuni enzimi hanno raggiunto la perfezione catalitica attraverso forze elettrostatiche che attraggono e guidano i substrati nel loro sito attivo. 
 
Negli enzimi cataliticamente perfetti, ogni collisione enzima-substrato produce un intermedio che si trasforma rapidamente in prodotti.

<ol>
	<li>Ahern, K., & Rajagopal, I. (2021, 6 marzo). Enzimi perfetti. Università statale dell'Oregon. https://bio.libretexts.org/@go/page/3036.</li>
	<li>Petterson, G. (1992). Ottimizzazione evolutiva dell'efficienza catalitica degli enzimi. Giornale europeo di biochimica, 206(1), 289-295.</li>
	<li>Bar-Even, A., Milo, R., Noor, E., & Tawfik, D. S. (2015). L'enzima moderatamente efficiente: incontri inutili e flaccidità enzimatica. Biochimica, 54(32), 4969-4977.</li>
</ol>

enzimi cataliticamente perfetti

La teoria degli enzimi cataliticamente perfetti fu proposta per la prima volta da W.J. Albery e J. R. Knowles nel 1976. Questi enzimi catalizzano le reazioni biochimiche ad alta velocità. I loro valori di efficienza catalitica vanno da 108-109 M-1s-1. Questi enzimi sono anche detti "a diffusione controllata" poiché l'unico passaggio limitante la velocità della catalisi è quello della diffusione del substrato nel sito attivo. Gli esempi includono trioso fosfato isomerasi, fumarasi e superossido dismutasi.

La maggior parte degli enzimi raggiunge la perfezione catalitica grazie ai gruppi carichi presenti sulla loro superficie che orientano e guidano il substrato nel sito attivo. Altri enzimi hanno una disposizione specifica del sito attivo, contribuendo alla perfezione catalitica. Negli enzimi come la superossido dismutasi, gli ioni metallici, come rame e zinco, nel sito attivo e gli amminoacidi carichi, come l'arginina, vicino al sito attivo accelerano la conversione dell'anione superossido in ossigeno e perossido di idrogeno. Mutazioni casuali negli enzimi favoriscono tali interazioni con i loro substrati e gli enzimi con maggiore efficienza vengono selezionati naturalmente nel tempo.

Gli enzimi perfetti non solo catalizzano reazioni altamente efficienti ma possono anche aiutare a proteggere le cellule dai dannosi intermedi di reazione. Ad esempio, la trioso fosfato isomerasi (TPI) è un enzima nella via glicolitica che catalizza l'interconversione del diidrossiacetone fosfato (DHAP) e della gliceraldeide 3-fosfato (G3P). La lenta conversione del DHAP in G3P forma un intermedio enediolo che alla fine si decompone in un composto tossico. Poiché il TPI è un enzima cataliticamente perfetto, accelera la reazione e trasforma rapidamente l'intermedio nel prodotto, evitando composti indesiderati. Finora, pochissimi enzimi si sono evoluti fino a raggiungere la perfezione catalitica. La maggior parte degli enzimi sono moderatamente efficienti.

Enzimi cataliticamente perfetti

La teoria degli enzimi cataliticamente perfetti è stata proposta per la prima volta da W.J. Albery e J. R. Knowles nel 1976. Questi enzimi catalizzano reazioni biochimiche a ...

Education

Didattica

JoVE Core

Cell Biology

Biologia cellulare

Unit 1

Unità 1

Energy and Catalysis

Energia e Catalisi

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

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

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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

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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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LS.Bio.1.1

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Diffusion-Controlled Enzymes and Reaction Speed

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