INTRODUCTION TO
ENZYMOLOGY
Dr. A. Mohammed
Introduction
• Enzymes are proteins that increase the rate of
reaction by lowering the energy of activation
• They catalyze nearly all the chemical reactions taking
place in the cells of the body.
• Not altered or consumed during reaction.
• Reusable
Introduction
• Enzymes play an important role in Metabolism,
Diagnosis, and Therapeutics.
• All biochemical reactions are enzyme catalyzed
in the living organism.
• Level of enzyme in blood are of diagnostic
importance e.g. it is a good indicator in disease
such as myocardial infarction, liver and kidney.
• Enzyme can be used therapeutically such as
digestive enzymes.
ACTIVE SITES
• Enzyme molecules contain a special pocket or
cleft called the active sites.
Xanthine Oxidase Active site
Gln 767- catalysis
Glu802- catalysis
Phe 914- binding
Phe 1009-
binding
Glu 1261-
catalysis
Arg 880- catalysis
Figure 2: Structure of the active site of bovine xanthine oxidoreductase
(source: Gadave et al., 2020)
Coenzymes and Cofactor
• The activity of some enzymes depends on nonprotein
organic molecules (e.g., coenzymes) or metal ions (e.g.,
cofactors) associated with the protein.
• Coenzymes are organic nonprotein compounds that bind
reversibly to certain enzymes during a reaction and function
as a co-substrate.
• Many coenzymes are vitamin derivatives.
• Nicotine adenine dinucleotide (NAD+), a derivative of
niacin, participates in many oxidation-reduction reactions
(e.g. glycolytic pathway).
• Tetrahydrofolate (THF), derived from folic acid, functions
in one-carbon transfer reactions (e.g., conversion of serine
to glycine).
Coenzymes and Cofactor
• cofactors are Metal ion that associate
noncovalently with enzymes and may help
orient substrates or function as electron
carriers.
• (1) Magnesium (Mg): kinases
• (2) Selenium (Se): glutathione peroxidase
• (3) Copper (Cu): oxidases e.g: cytochrome oxidase (transfers
electrons to oxygen to form water)
Properties of enzymes
1. Enzymes are specific
2. Enzymes speed up chemical reactions by lowering activation
energy
3. Enzymes are not changed permanently by the reaction they
catalyze but can undergo a transition state.
Enzyme Specificity
• Enzymes have varying degrees of specificity
for substrates
• Enzymes may recognize and catalyze:
- a single substrate
- a group of similar substrates
- a particular type of bond
Enzymes speed up chemical reactions
by lowering activation energy
• All chemical reactions require some amount of
energy to get them started.
OR
• It is First push to start reaction.
This energy is called activation energy.
Enzymes
Lower a
Reaction’s
Activation
Energy
Factors affecting the rate of a enzyme reaction
• Three factors:
1. Environmental factors
2. Cofactors and Coenzymes
3. Enzyme Inhibitors
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1. Environmental factors
A. Temperature: Extreme Temperature are
the most dangerous may denature
(unfold) the enzyme.
B. pH (most like 6 - 8 pH near neutral)
C. substrate concentration .
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Environmental factors
• Optimum temperature The temp at which
enzymatic reaction occur fastest.
Effects of temperature on enzyme activity
Environmental factors
• pH also affects the rate of enzyme-
substrate complexes
– Most enzymes have an optimum pH of
around 7 (neutral)
• However, some prefer acidic or basic conditions
Substrate Concentration and Reaction Rate
• The rate of reaction increases as substrate
concentration increases (at constant enzyme
concentration)
• Maximum activity occurs when the enzyme is
saturated (when all enzymes are binding substrate)
2. Cofactors and Coenzymes
• Inorganic substances (zinc, iron) and
vitamins (respectively) are sometimes need
for proper enzymatic activity.
• Example:
Iron must be present in the quaternary
structure - hemoglobin in order for it to
pick up oxygen.
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2. Cofactors and Coenzymes
• Coenzymes are vitamin derivatives like Mg is
needed for proper function of the enzyme
glutamine synthetase for the conversion of
glutamate to glutamine
3. Enzyme Inhibitors
• Enzyme activity are inhibited or regulated
1. Allosteric Control
2. Covalent Modification
Enzymes classifications
• The name of an enzyme in many cases end in –ase
• For example, sucrase catalyzes the hydrolysis of sucrose
• The name describes the function of the enzyme
For example, oxidases catalyze oxidation reactions
• Sometimes common names are used, particularly for the
digestion enzymes such as pepsin and trypsin
• This led to ambiguity in enzyme namings
the International Union of Biochemists (I.U.B.)
Classified enzymes into six functional Classes
(EC number Classification)
on the Basis of the Types of
Reactions That They Catalyze
• EC 1. Oxidoreductases
• EC 2. Transferases
• EC 3. Hydrolases
• EC 4. Lyases
• EC 5. Isomerases
• EC 6. Ligases
Oxidoreductases, Transferases and Hydrolases
Lyases, Isomerases and Ligases
Mechanism of Action of Enzymes
• Enzymes increase reaction rates by
decreasing the Activation energy:
• Enzyme-Substrate Interactions:
‒ Formation of Enzyme substrate
complex by:
‒ Lock-and-Key Model
‒ Induced Fit Model
Lock-and-Key Model
• In the lock-and-key model of enzyme action:
- the active site has a rigid shape
- only substrates with the matching shape can fit
- the substrate is a key that fits the lock of the active site
• This is an older model, however, and does not work for all
enzymes
Lock-and-Key Model
• In the lock-and-key model of enzyme action:
- the active site has a rigid shape
- only substrates with the matching shape can fit
- the substrate is a key that fits the lock of the
active site
This explains enzyme
specificity
This explains the loss
of activity when
enzymes denature
Induced Fit Model
• In the induced-fit model of enzyme action:
- the active site is flexible, not rigid
- the shapes of the enzyme, active site, and substrate adjust
to maximumize the fit, which improves catalysis
- there is a greater range of substrate specificity
• This model is more consistent with a wider range of enzymes
