biochemistry (lippincott's illustrated reviews series), 6e
DESCRIPTION
Enzymes Almost every reaction that happen in the body involves enzymes They function as a catalyst from physiological reaction Enzymes control in a selective manner reactants in chemical reactions These reactants are called substrate Consequently, Enzymes mediate all metabolic interactions in the bodyTRANSCRIPT
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Enzymes
OMAR A. ALOMAIRBiochemistry 1
ReferencesBiochemistry (Lippincott's Illustrated Reviews Series), 6E
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Enzymes
• Almost every reaction that happen in the body involves enzymes
• They function as a catalyst from physiological reaction
• Enzymes control in a selective manner reactants in chemical
reactions
• These reactants are called substrate
• Consequently, Enzymes mediate all metabolic interactions in the
body
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EnzymesNomenclature
• Enzymes are usually named in two ways
• The first one is the “Recommended naming system”
• This naming scheme is more appropriate and easier for every day use
• The second is the “Systematic naming system”
• This naming scheme is more complicated and is required to accurately
describe an enzyme
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EnzymesNomenclature “Recommended naming system”• The commonly encountered enzymes are giving the suffix “ase”
• The “ase” suffix is linked the substrate of the reaction, e.g.
glucosidase and urease
• Or it is attached to the characteristic of the chemical reaction, e.g.
lactate dehydrogenase and adenylyl cyclase
• However, a number of enzymes are usually named arbitrarily
without a description of their functions, e.g. trypsin and pepsin
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EnzymesNomenclature “Systematic naming system”• According to this nomenclature, all enzymes are classified under 6
classes
• For any enzyme, the suffix “ase” is part of the chemical
modification initialed by the enzyme
• Additionally, all the involved substrates written a head of the
chemical reaction, e.g. lactate :NAD+ oxidoreductase
• Although this naming scheme is very informative, it can be a bit
confusing and unwieldy
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EnzymesNomenclature “Systematic naming system”
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EnzymesNomenclature “Systematic naming system”
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EnzymesProperties: 1. Active site specificity• Each enzyme has a unique empty space within its structure
named the active site
• The active site contains amino acids portion that participate in the
substrate interactions to form enzyme–substrate (ES) complex
• This binding catalyzes the substrate via structural transformation
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EnzymesProperties: 1. Active site
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EnzymesProperties: 2. Catalytic efficiency• Efficiency is one of the most important properties of enzymes
•When enzymes are not catalyzing a reaction, it takes 108 longer
• The amount of byproduct that results from the catalytic reaction is
called the turnover number
• This number range between 102-104 product per second
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EnzymesProperties: 3. Coenzymes and Cofactors• Some enzymes can not facilitate a catalytic reaction with a
substrate without the presence of certain molecules
•When these molecules composed of metallic ions such as Zn2+ or
Fe2+, it is called cofactors
• On the other hand, if the extra molecules organic in nature it is
denoted as coenzymes. E.g. vitamins B1
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EnzymesProperties: 3. Location• Enzymatic reactions take place in specific location within a cell
• This aspect of enzyme compartmentalization provide the specify
of enzymes
• Since there are thousands of enzymes within a cell, isolating
enzymes from their substrates into specific organelles helps in
organizing the huge number of pathways
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EnzymesProperties: 3. Location
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EnzymesFactors affecting rate of reaction1. Substrate concentration• The velocity of the rate of reaction (V) is equal to “the number of
substrate molecules converted to product per unit of time”
• The of products produced keep forming is proportional to the
substrate concentration
• This increase in the rate enzymatic reaction is limited by the
maximum velocity of the reaction and not the substrate
concentration
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EnzymesFactors affecting rate of reaction1. Substrate concentration
Enzyme 1
Enzyme 2
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EnzymesFactors affecting rate of reaction2. Temperature• Until a maximum velocity is reached, the velocity of enzymatic
reaction is increased as the temperature increases
• This is due to the increase the amount of substrate complex
having sufficient energy
• Any further increase in the temperature will retard the rate of the
reaction
• The reason behind this is the denaturation of the enzyme
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EnzymesFactors affecting the rate of reaction1. Temperature
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EnzymesFactors affecting the rate of reaction3. pH• Reaction velocity is controlled by the concentration of (H+)
• The catalytic activity of enzyme require the targeted chemical
group to be in a specific ionized form
• Similar to high temperature, extreme pH value can slow the rate
of reaction due to the degradation of the enzyme itself
• Each enzyme has preferred range of pH within the body
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EnzymesFactors affecting the rate of reaction3. pH
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EnzymesInhibition• Inhibitors are any substance that interfere with the enzymatic
reaction
• These inhibitors can be irreversible when it form a covalent bond,
e.g. Lead binds covalently with ferrochelatase preventing heme
synthesis
• They can also be reversible when covalent binding is not a factor
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EnzymesReversible Inhibition• Reversible inhibition can be classified to either competitive or
non-competitive inhibition
• Competitive inhibitors occupy the site of the substrate
• Non-competitive inhibitors bind to a different site form the
substrate
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EnzymesReversible Inhibition
Competitive inhibitionNon-Competitive
inhibition
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EnzymesClinical Applications• Different enzymes are released from different part of the body
• The level of the enzyme in circulatory system can be correlated to
a number of disease
• Enzyme level in serum can be quantified and compared to normal
levels
• For example, the enzyme alanine aminotransferase (ALT) presence
at high level in blood is an indication of liver disease
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EnzymesClinical Applications
Enzyme level in blood