Download Enzymes -2.Properties, claasification and theories of action (1)

Enzymes-2 – Properties, classification and theories of action
lecture NO : 1st MBBs
Dr Muhammad Ramzan
Properties – the definition
• Any measureable aspect of the system that is essential to
maintain the material structure of life
• The property can Physical like size shape and :
• Chemical like nature of the molecule Protein CHO, Lipids and
Nucleic acid
The properties of enzymes
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Followings are the enzymes‘ properties
The nature .
Activation energy and Active site
Catalytic efficiency and Enzyme specificity
Regulation of enzyme activity
Distribution/location of enzyme
Site of synthesis and action
Nature of the Enzymes
• All the enzymes are proteins that ↑ the velocity of a chemical
reaction and are not consumed during the reaction
• Some of the RNAs also act as enzymes like rRNAs- Ribozymes
that are involved in protein synthesis
• These RNAs establish peptide bond B/W the Amino acids of
the Product proteins
Activation energy
• It is the minimum amount of energy required to Initiate and
complete a catalyzed chemical reaction
• Enzymes reduce the activation energy to make the reactants
• (Enzyme and Substrate) to bind for ESC :
• and transformed into Products
• It is much lower than required for the non catalyzed reactions
Active site – Has functional/Amino Acyl groups
(2-4 AAs)
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Active sites are the pockets/hollows on the surface of E that
assumes 3D shape after protein folding
Active site contains the side chains of the AAs (amino Acyl or
functional groups 2 - 5 AAs) that are involved in the :
Substrate binding and Catalysis
Binding of S to active site produces ESC which is cleaved to
products and enzyme .
Both are released and enzyme can be reused
Active site
Catalytic efficiency
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Es are the efficient catalysts and can ↑ the rate of chemical
reaction up to 103 to 108 than the uncatalysed reaction
• About 100 to 1000 substrates are transformed into the
products / unit time
• Turnover number is the maximum no: of substrates converted
into products/ active site/ unit time
• Turn over no: of Carbonic Anhydrase is 36million/active site/minute
Enzyme specificity
• Enzymes are highly specific and interact with specific substrates
with specific functional groups
• Other substrates would not fit into their active sites
• It catalyzes only one type of chemical reaction
• The set of enzymes present in a cell determines which type of
reaction will occur in that cell
Cofactors - property of enzymes
non protein parts of E
• Cofactors are the non protein components of an enzyme and
is essential for E activity
• Halozyme is an active enzyme with protein and a cofactor
• There are 2 types of cofactors that bind to the active site
• Inorganic metallic ions : like Iron, Magnesium and Zinc.
• Also called as Co factors
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• Organic molecules: like Co A; NAD,NADH and FAD
• Also called as Coenzymes
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Regulation of enzyme activity
• Enzyme activity can be regulated
• Cell regulates the activity of the enzyme according to their
demand and need through E activation or inhibition
• Like Glycogen Synthase is active when there is excess of glucose
and body needs to store CHOs as Glycogen
• Its activity is inhibited when there is hypoglycemia
Distribution/Location of enzymes 1
Intra/Extra cellular
• Majority of the E are intracellular except digestive enzymes
which are present in the lumen of GIT
• Enzymes are also localized in the specific organelles called
compartmentalization like Mitochondria that :
• House the enzymes for FA oxidation and Citric acid cycle
• Intra cellular Es are secreted in small and Extra cellar in large quantities
Location of enzymes 2
• Cytosole has the enzymes for Glycolysis, Fatty acid synthesis
and HMP pathway
• Lysosomes contain the enzymes (Hydrolases) for the :
• Degradation of macromolecules like TG; Proteins, Glycogen
and Nucleic acids
• Compartmentalization provides the favorable environment
for the reactions to occur
Site of synthesis/action
reused and measured
• The site of synthesis and action is the same
• A small amount of E is required for catalysis
• Enzymes can be reused and measured for diagnostic and
monitoring (treatment) purposes
Classification of enzyme – by adding suffix - "ase"
• Es are commonly named by adding the suffix "-ase" to the root
name of the substrate molecule it is acting upon.
• For example, Lipase catalyzes the hydrolysis of lipids/TG
• Sucrase catalyzes the sucrose into Glucose and fructose
• A few enzymes discovered before this naming system are
known by their common names
• Examples are the Pepsin and Trypsin which catalyze the proteins .AAs
Classification of enzymes – IEC
Based upon type of reaction
• The latest systematic nomenclature system known as the
International Enzyme Commission (IEC) system
• is based upon the type of reaction catalyzed.
• There are six broad groups of enzymes in this system
Classification of enzymes - Reaction types
Enzyme action – theories or Models
Active site is common to all E
• Enzymes differ widely in structure and specificity, but a
general theory that accounts for their catalytic behavior
• is widely accepted. Like :
• The enzyme and its substrates interact only over a small
region over the surface of the enzyme
• called the Active site.
Theories /models of enzyme action. 3
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There are 3 theories about mechanism of E action with minor
difference of the flexibility or rigidity of the Active site and
changes in the conformation/shape of :
Enzyme, substrate and active site
Lock and key Theory
Induced – fit theory
The Transition – State Model/Theory
Lock and key theory
• The lock-and-key theory explains the high specificity of E activity.
- Enzyme surfaces accommodate substrates, having specific
shapes , sizes and functional groups
– So only specific substances ― fit in an active site to form
• a ES complex.
Limitation of Lock and key theory
Rigid E conformation
• A limitation of this theory is that it requires enzymes
• conformations to be rigid and so is the (active site)
• Research suggests that enzymes conformations are not so
rigid but some what flexible.
Enzyme – Lock and key model
Induced fit model/theory
E/active site changes to S
• This model is the more accepted for enzyme-substrate
complex than the lock-and-key model.
• It shows that enzymes are rather flexible structures in
which the active site continually reshapes by:
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Its interaction with the substrate until the substrate is
completely bound to it.
• Which is also the point at which the final form and shape
of the enzyme is determined.
Enzyme – Induced – fit model
Transition- state Theory - TST
S to activated Complex
• Transition state theory begins with binding of the Substrate to
the active site of the enzyme
• There is a change in the Geometry of the S after E binding to
assume a state that is neither a product nor ESC
• This transition/activated complex undergoes catalysis to products
• The demerit is the high cast of energy
Transition state Model/Theory -TST
Transition state/activated state theory