Enzymes Overview 2013 STUDENT
Transcript of 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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General Properties of Enzymes
Holoenzyme
Functional unit
Consists of:
Apoenzyme
Cofactor/coenzyme
Proenzyme/zymogen
Inactive enzyme
Holoenzyme
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General Properties of Enzymes
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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Definitions and Related Terms
Allosteric site
Non-active site
May interact with other
substances resulting inoverall enzyme shape
change
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Definitions and Related Terms
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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Definitions and Related Terms
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