enzymes overview 2013 student

7/27/2019 Enzymes Overview 2013 STUDENT

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MLAB 2401: Clinical Chemistry

Keri Brophy-Martinez

Enzymes: Overview


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Enzymes

Functional proteins that catalyse biological

reactions

Involved in all essential body reactions

Found in all body tissues

Seen in serum following cellular injury or from

degraded cells

Decrease the amount of free energy needed

to activate a specific reaction


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General Properties of Enzymes

Not altered or consumed during reaction

Reusable

Accelerate speed of reactions


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Holoenzyme

Functional unit

Consists of:

Apoenzyme

Cofactor/coenzyme

Proenzyme/zymogen

Inactive enzyme

Holoenzyme


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Role

Increase reaction rates while not being consumed

or altered

Enzyme

Substrate Product


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Definitions and Related Terms

Active site

Specific area of the

enzyme structure that

participates in the

reaction(s)/interacts

with the substrate


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Allosteric site

Non-active site

May interact with other

substances resulting inoverall enzyme shape

change


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Isoenzymes

Structurally different enzymes that catalyze the

same reaction

Multi molecular form

Similar catalytic activity

Differing biochemical or immunological characteristics

Can detect by different electrophoresis patterns,

absorption patterns, or reaction with specific

antibodies


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Cofactor

Non-protein substances required for normal

enzyme activity

Types

Activator: inorganic material such as minerals (Ca 2+, Fe2+)

Co-enzymes: organic in nature (ATP, ADP, nicotinamide)


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Enzyme Kinetics

Reactions occur spontaneously if energy is

available

Enzymes lower the activation energy for the

chemical reactions


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Enzyme Kinetics

Activation energy

Excess energy that

raises all molecules

at a certain

temperature to the

activation state


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Enzyme Kinetics

Basic reaction

S + E ES E + P

Where S= substrate

Substance on which the enzyme acts

E= Enzyme

ES= enzyme-substrate product Physical binding of a substrate to the active site of enzyme

P= Product


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Enzyme Kinetics & Specificity

Enzymes differ in their ability to react with differentsubstrates

Absolute specificity

Enzyme combines with only one substrate and catalyzes one

reaction

Group specificity

Combine with all substrates containing a specific chemical group

Bond specificity

Enzymes specific to certain chemical bonds Stereoisomerism

Enzymes that mainly combine with only one isomer of a particularcompound


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Michaelis-Menten

Relationship of thereaction velocity/rate tothe substrateconcentration

The Michealis-MentenConstant(Km)

The substrateconcentration in molesper liter when the initialvelocity is V max.

Michaelis-Menten Curve


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Michaelis-Menten

First order kinetics

Rate is directly

proportional to substrate

concentration

Zero order kinetics

Plateau is reached

depends only on enzyme

concentration


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Michaelis-Menten

Equation used to distinguish different kinds ofinhibition

Where V0: velocity/rate of enzymatic activity

Vmax: The maximal rate of reaction when the enzymeis saturated

Km: (constant)the substrate concentration thatproduces of the maximal velocity

S: substrate concentration


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Lineweaver-Burk Plot

Adaptation of

Michaelis-Menten

equation

Yields a straight line


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Influencing Factors on Enzymatic

Reactions Substrate Concentration

Enzyme Concentration

The higher the enzyme level, the faster the reaction

pH

Most reaction occur in range of 7.0-8.0

Changes in pH can denature an enzyme

Temperature

Most reactions performed at 37 o C

Increasing temp increases rate of reaction

Avoid high/low temps due to denaturation of enzyme

Cofactors Influence the rate of reaction

Inhibitors

Presence can interfere with a reaction can be reversible or irreversible


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Types of Inhibition

Competitive

Any substance that competes with the substrate

for the active binding sites on the substrate

Reversible

Non-competitive

Any substance that binds to an allosteric site

Uncompetitive

Inhibitors bind to the ES complex

No product produced


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Noncompetitive

Inhibition

Irreversible

InhibitionCompetitive

Inhibition


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Types of Inhibition

Competitive NoncompetitiveUncompetitve


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Enzyme Nomenclature

Historical

ID of individual enzymes was made using thename of the substrate that the enzyme acted

upon and adding ase as the suffix Modifications were often made to clarify the

reaction

International Union of Biochemistry (IUB) in 1955

appointed a commission to study and makerecommendations on nomenclature forstandardization


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Enzyme Nomenclature: IUB

Components

Systematic name

Describes the nature of the reaction catalyzed

Example: alpha 1,4-glucagon-4-gluconohydrolase

Recommended name

Working or practical name

Example: amylase

Numerical code

First digit places enzyme in a class

Second and third digit represent subclass(s) of the enzyme

Fourth digit specific serial number in a subclass

Example: 3.2.1.1


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Enzyme Nomenclature: IUB

Standard Abbreviated name

Accompanies recommended name

Example: AMS

Common Abbreviated name

Example: AMY


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Enzyme Classification: General

Plasma vs. non-plasma specific enzymes

Plasma specific enzymes have a very definite/

specific function in the plasma

Plasma is the normal site of action

Concentration in plasma is greater than in most tissues

Often liver synthesized

Examples: plasmin, thrombin


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Enzyme Classification: General

Non-plasma specific enzymes have no known

physiological function in the plasma

Some are secreted in the plasma

Increased number of this type seen with cell disruptionor death


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Enzyme Classification

Six classes

Oxidoreductases

Involved in oxidation-reduction reactions

Examples: LDH, G6PD

Transferases

Transfer functional groups from one substrate to another

Examples: AST, ALT

Hydrolases Catalyze the hydrolysis of various bonds

Examples: acid phophatase, lipase


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Enzyme Classification

Lyases

Catalyze removal of groups from substrates without

hydrolysis, product has double bonds

Examples: aldolase, decarboxylase Isomerases

Involved in molecular rearrangements

Examples: glucose phosphate isomerase

Ligases

Catabolism reactions with cleavage of ATP

Example: GSH


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References

Bishop, M., Fody, E., & Schoeff, l. (2010). Clinical Chemistry:

Techniques, principles, Correlations. Baltimore: Wolters

Kluwer Lippincott Williams & Wilkins.

http://regentsprep.org/Regents/biology/units/homeostasis/p

rocesses.cfm

http://student.ccbcmd.edu/~gkaiser/biotutorials/proteins/fg9

.html

Sunheimer, R., & Graves, L. (2010). Clinical Laboratory

Chemistry. Upper Saddle River: Pearson .
http://student.ccbcmd.edu/~gkaiser/biotutorials/proteins/fg9.htmlhttp://student.ccbcmd.edu/~gkaiser/biotutorials/proteins/fg9.htmlhttp://student.ccbcmd.edu/~gkaiser/biotutorials/proteins/fg9.htmlhttp://student.ccbcmd.edu/~gkaiser/biotutorials/proteins/fg9.html

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