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Factors that Affect Enzyme Activity

SBI4U

Enzymes

+Factors that Affect Enzyme Activity (reaction rate)

The factors we will test for the enzyme lab are:

pH

temperature

substrate concentration

enzyme concentration

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Enzyme is said to be denatured – no longer a catalyst

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Enzyme is said to be denatured – no longer a catalyst

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Other Regulators of Enzyme Activity

Enzyme Cofactors Non-protein, bound to enzyme

May be organic or inorganic ions

Enhance enzyme activity - “helper”change enzyme active site shapemake active site more reactive

Examples of Inorganic Cofactors

Mg in Chlorophyll

Fe in heme group of hemoglobin

Organic CofactorsActive site

Enzyme

Active site

Enzyme

Prosthetic group(perm. attached)

Coenzyme(detaches)

Prosthetic Groups

Coenzymes

e.g., FAD

e.g., NAD

Important Organic CofactorsNicotinamide Adenine Dinucleotide (NAD)

coenzyme derived from vitamin B3

carries and transfers electrons and functions as oxidizing agent in redox reactions

Active site

Enzyme

Coenzyme(detaches)

Coenzyme

e.g., NAD

Important Organic CofactorsFlavin Adenine Dinucleotide

(FAD)

prosthetic group

like NAD, FAD functions as a reducing agent in cellular respiration and donates electrons to the electron transport chain

Active site

Enzyme

Prosthetic group(perm. attached)

Prosthetic Group

e.g., FAD

+Covalent Modulation

Enzymes can be activated or inactivated by covalent modification.

A common example is phosphorylation of an enzyme (addition of a phosphate group to the amino acids serine, threonine, or tyrosine) mediated by another enzyme called a kinase .

The phosphorylation is reversible, and other enzymes called phosphatases typically catalyze the removal of the phosphate group from the enzyme.

+Covalent Modulation

HSL

Fasting/exercise

Hormone-sensitive lipase (HSL)is phosphorylated during fasting or exercise to catalyze the hydrolysis of TGs to release FAs

HSL + H2O (hydrolysis)

FA

FA

FAFA

Triglyceride (TG)

FAFA Diglyceride

- acti

vated

enzyme

+Enzyme Inhibitors

Enzymes may become deactivated

Temporarily or Permanently

Types of InhibitorsReversible InhibitorsIrreversible Inhibitors

+Reversible Inhibitors

Used to control enzyme activity

Involves the substrate or the end product of the reaction

For example: a build up of the end product – called feedback inhibitionhttp://highered.mcgraw-hill.com/classware/ala.do?alaid=ala_1032273

+Competitive Inhibitors Competitive Inhibitors have a similar shape as the substrate

Compete with the substrate to bind to the active site, but no reaction occurs

Block the active site so no substrate can fit

Competitive Inhibition

+Non-Competitive Inhibitors Binds to a different site on the enzyme

Does not compete with the substrate to bind to the active site

Two ways to non-competitively inhibit the enzyme:1. slow down the reaction or 2. changes the shape of the active site (allosteric inhibition)

Which of the following diagrams represents allosteric inhibition?

(a) Reaction

enzyme

active site

Substrate binds with the active site of enzyme

Reaction occurs and product molecules are produced(b) Inhibition

enzyme

Inhibitor

active site

Substrate

Substrate

Inhibitor binds with the inhibitor site of the enzyme and changes the structure of the active site

Inhibitor prevents binding of the substrate by changing the active site shape

+(a) ReactionSubstrate

enzyme

Inhibitor site

active site

Substrate binds with the active site of enzyme

Reaction occurs and product molecules are produced

enzyme

Inhibitor site

Inhibitor

active site

Inhibitor binds with the inhibitor site of the enzyme

Substrate may still bind with the enzyme but the reaction rate is reduced

(b) Inhibition

Recap - Distinguish between competitive and non-competitive inhibition

Competitive

inhibitor competes with the substrate for binding to the active site of the enzyme and prevents reaction

Non-competitive

inhibitor does not compete for the active site,

binds to a different site,

either slows down or completely prevents reaction.

Recap cont. Explain how allosteric inhibitors differ from other non-competitive inhibitors:

While non-competitive inhibitors reduce enzyme activity and slow down the reaction rate, allosteric inhibitors block the active site altogether and prevent its functioning completely

+Irreversible Inhibitors

Also called poisons

For example: certain heavy metalsE.g., cadmium, lead, mercury

Retained in the body and lost slowly

Cyanide is a poison that prevents the activity of cytochrome C oxidase, an enzyme in the electron transport chain in the cell. It therefore inhibits ATP production and cellular respiration.

Cytochrome c oxidase

Why are enzymes so tightly regulated by co-factors and inhibitors?

Control of Metabolism Biochemical reactions are controlled in part by the specificity of

substrate binding, but the human body could not function if all enzymes were present together and all operating maximally with no regulation.

There would be biochemical chaos with substances being synthesized and degraded at the same time.

Instead, the body tightly regulates enzymes through metabolic pathways and by controlling specific enzymes within a pathway.

This approach allows an entire pathway to be turned on or off by simply regulating one or a few enzymes.

Metabolic pathways can also be regulated by switching specific genes on or off.

Since the tight control of enzyme activity is essential for homeostasis, any malfunction (mutation, overproduction, underproduction or deletion) of a single critical enzyme can lead to a genetic disease.

Lethal illness can be caused by the malfunction of just one type of enzyme out of the thousands of types present in our bodies.

E.g., the disease phenylketonuria (PKU) results from a mutation of a single amino acid in the enzyme phenylalanine hydroxylase, which catalyzes the first step in the degradation of phenylalanineThe result is a build-up of phenylalanine and related products and can lead to a number of ill effects

Enzymes play a critical role in everyday life. Many heritable genetic disorders occur because there is a

deficiency or total absence of one or more enzymes. Routine medical tests monitor the activity of enzymes in the

blood,involve the use of enzymes to diagnose diseases, and many of the prescription drugs (e.g., penicillin,) exert their effects through interactions with enzymes.

Enzymes and their regulators are important tools in medicine, agriculture, and food science. The application of enzymes in food processing and pharmaceuticals is a

multi-billion dollar industry! Biotechnology is influencing countless aspects of our daily lives. The use and impact of enzymes in these sectors will be the focus of your biochemistry unit task.

Why is it important to know how enzymes are regulated?