Download CHAPTER 1: ENZYME KINETICS AND APPLICATIONS (Part 1a

CHAPTER 1:
ENZYME KINETICS AND APPLICATIONS
(Part 1a : Kinetics of Enzyme Catalyzed Reactions)
ERT 317 Biochemical Engineering
Sem 1, 2016/2017
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Role of Biochemical /Bioprocess
Engineer
•
•
•
•
exploit advances in biology to create new products
design biochemical processes & operate plants
develop energy resources
Develop new, environmentally friendly, and safer
processes to make the biochemical products that people
depend on.
• Work in research and development laboratories,
creating polymeric materials with improved performance
and durability.
• Work in manufacturing, making vaccines and antibiotics.
• Invent new ways to keep our food and water supplies
safe.
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Bioprocess Engineer’s Task
– Minimize production of unwanted
byproducts
– Separate the good (product) from
the bad (byproducts)
– Recover the unused reactants
– Maximize profit, minimize energy
consumption
– Minimize impact on the
environment
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OUTLINE
• Introduction
• Enzyme Structure
• Enzyme Function
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Enzymes
•
There are many chemical compounds in the living cell.
•
How they are manufactured and combined at sufficient
reaction rates under relatively mild temperature and
pressure?
•
How does the cell select exactly which reactants will be
combined and which molecule will be decomposed?
Catalysis by ENZYME
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Enzymes
•Enzymes are biological catalysts that are protein molecules in
nature- react in mild condition
•They are produced by living cells (animal, plant, and
microorganism) and are absolutely essential as catalysts in
biochemical reactions.
•Almost every reaction in a cell requires the presence of a
specific enzyme– related to its particular protein structure.
•A major function of enzymes in a living system is to catalyze
the making and breaking of chemical bonds.
•Therefore, like any other catalysts, they increase the rate of
reaction without themselves undergoing permanent chemical
changes.
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 Over 2000 enzymes have been identified
 Often named by adding the - ‘ase’ to the name of
substrate acted upon, or the reaction catalyzed
such as urease, alcohol dehydrogenase
 The majority of cellular reactions are catalyzed by
enzymes
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 Some protein enzyme required a non-protein group for their activity.
 Non protein group:
 Cofactors: metal ions, Mg, Zn, Mn, Fe.
 Coenzyme: complex organic molecule, NAD, FAD, CoA
 Vitamins
 Catalyze biochemical reactions
 breaking, forming and rearranging bonds.
 Catalytic function – very specific and effective (Specific because of
conformational shape)
 Dictated by the enzyme active site.
 Some active sites allow for multiple substrates.
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• Enzymes are catalysts
– Catalyst: chemical that changes the rate of a reaction without
being consumed
– Recycled (used multiple times)
• Enzymes reduce the activation energy of a reaction
– Amount of energy that must be added to get a reaction to
proceed
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Catalysts
• A catalyst is unaltered during the course of a reaction and functions in
both the forward and reverse directions.
• In a chemical reaction, a catalyst increases the rate at which the reaction
reaches equilibrium.
• For a reaction to proceed from starting material to product, the chemical
transformations of bond-making and bond-breaking require a minimal
threshold amount of energy, termed activation energy.
• Generally, a catalyst serves to lower the activation energy of a particular
reaction.
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Enzyme Function
Enzymes lower the activation energy of reaction catalyzed
( They do this by binding to the substrate of the reaction, and
forming an enzyme-substrate (ES) complex)
Substrate binds to a specific site on the enzyme called the active
site
Multi-substrate reactions possible
 ‘Lock and key’ model
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The activation
energy for the
decomposition of
hydrogen
peroxide varies
depending on the
type of catalysis.
Type of catalysis
Activation
energy
Uncatalyzed
reaction at 20°C
18
kcal/mol
Enzymatically
catalyzed
(catalase)
7 kcal/mol
Chemically
catalysed (by
collodial
platinum)
13
kcal/mol
Enzyme lower the activation energy of the reaction by binding
the substrate and forming an enzymes-substrate complex.
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Comparison of activation energies in the uncatalyzed and
catalyzed decompositions of ozone.
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Important Terms To Be Remember!
• active site - a region of an enzyme comprised of different amino
acids where catalysis occurs or a small portion of the surface of
an enzyme which a specific chemical reaction is catalyzed
• substrate - the molecule being utilized and/or modified by a
particular enzyme at its active site
• co-factor - organic or inorganic molecules that are required by
some enzymes for activity. These include Mg2+, Fe2+, Zn2+ and
larger molecules termed co-enzymes like nicotinamide adenine
dinucleotide (NAD+), coenzyme A, and many vitamins.
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Types of Enzymes
• holoenzyme - a complete, catalytically active enzyme
including all co-factors OR an enzyme containing a non
protein group
• apoenzyme - the protein portion of a holoenzyme minus the
co-factors OR the protein part of holoenzyme
• (holoenzyme = apoenzyme+cofactor)
• isozyme - (or iso-enzyme) an enzyme that performs the same
or similar function of another enzyme that occur in several
different molecular forms.
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Nomenclature of enzyme
Originally enzymes were given non descriptive names such as:
rennin : curding of milk to start cheese-making processor
pepsin : hydrolyzes proteins at acidic pH
trypsin : hydrolyzes proteins at mild alkaline pH
The nomenclature was later improved by adding the suffix -ase to the name of the substrate with which the
enzyme functions, or to the reaction that is catalyzed, for example:
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Alcohol
dehydrogenase
Glucose isomerase
Glucose oxidase
Lactic acid
dehydrogenase
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Enzyme reactions are different from
chemical reactions, as follows:
1. An enzyme catalyst is highly specific, and catalyzes only one or
a small number of chemical reactions. A great variety of enzymes
exist, which can catalyze a very wide range of reactions.
2. The rate of an enzyme-catalyzed reaction is usually much faster
than that of the same reaction when directed by nonbiological catalysts
at mild reaction condition.
3. A small amount of enzyme is required to produce a desired effect.
4. Enzymes are comparatively sensitive or unstable molecules
and require care in their use.
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Enzymatic Reaction Principles
• Biochemically, enzymes are highly specific for their substrates and
generally catalyze only one type of reaction at rates thousands and
millions times higher than non-enzymatic reactions.
• Two main principles to remember about enzymes are :
a) they act as CATALYSTS (they are not consumed in a
reaction and are regenerated to their starting state)
a) they INCREASE the rate of a reaction towards equilibrium
(ratio of substrate to product), but they do not determine the
overall equilibrium of a reaction.
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Reaction Rates
 The rate of the reaction is effected by several factors
including the concentration of substrate, temperature and
pH.
 For most standard physiological enzymatic reactions, pH
and temperature are in a defined environment (eg; pH 6.97.4, 37oC).
 This enzymatic rate relationship has been described
mathematically by combining the equilibrium constant, the
free energy change and first or second-order rate theory.
Keq = e−∆Go/RT
 The net result for enzymatic reactions is that the lower the
activation energy, the faster the reaction rate, and vice versa.
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Specificity
• Most synthetic catalyst are not specific
i.e., they will catalyze similar reactions
involving many different kinds of
reactants.
• While enzymes are specific. They will
catalyze only one reaction involving only
certain substances.
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Binding Energy
• The interaction between enzyme and its
substrate is usually by weak forces.
• In most cases, Van der Waals forces and
hydrogen bonding are responsible for
the formation of ES complexes.
• The substrate binds to a specific site on
the enzyme known as the active site.
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Classification of Enzyme
Enzymes fall into 6 classes based on function
1.
Oxidoreductases: which are involved in oxidation, reduction, and
electron or proton transfer reactions
2.
Transferases : transfer of functional group
3.
Hydrolases : which cleave various covalent bonds by hydrolysis
4.
Lyases : catalyse reactions forming or breaking double bonds
5.
Isomerases : catalyse isomerisation reactions
6.
Ligases : join substituents together covalently.
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References
• Shuler, M. L. and Kargi, F. (2014). Bioprocess Engineering: Basic
Concept. 2nd Ed. Upper Saddle River, NJ: Prentice Hall PTR
• Rao, D.G. (2010). Introduction to Biochemical engineering. 2nd Ed.
Tata McGraw Hill Education Private Limited
• Dutta, R. (2008). Fundamentals of Biochemical Engineering. New Delhi:
Ane Books India
• Katoh, S. and Yoshida, F. (2009). Biochemical Engineering: A Textbook
for Engineers Chemists and Biologists. Weinheim: Wiley-VCH Verlag
GmbH & Co
• Nielsen, J., Villadsen, J. and Gunner L. (2011). Bioreaction Engineering
Principles. 3rd Ed. New York: Springer Science+Bussiness Media
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