2. WHAT IS AN ENZYME?
• ENZYMES ARE “BIOCATALYSTS”.
• THEY ARE BIOLOGIC POLYMERS THAT
CATALYSE VARIOUS CHEMICAL
REACTIONS IN THE BODY THAT HELPS
TO MAINTAIN LIFE.
• ENZYME CATALYSIS IS VERY RAPID.
• LACK CAN CAUSE VARIOUS INBORN
ERRORS OF METABOLISM.
4. PROPERTIES OF ENZYMES
• ENZYMES ARE PROTEIN IN NATURE(EXCEPTION:-
RNA ENZYMES(RIBOZYMES))
• THEY ARE HEAT LABILE.
• CAN BE PRECIPITATED BY PROTEIN
PRECIPITATING AGENTS
• 16 % WEIGHT IS OF NITROGEN.
5. CLASSIFICATION OF ENZYMES
• To address the ambiguities , the International Union of
Biochemists developed an unambiguous system of
enzyme nomenclature in which each enzyme has a
unique name and code number that identify the type of
reaction catalysed and the substrates involved.
• Enzymes are grouped into six classes:-
• OXIDOREDUCTASES
• TRANSFERASES
• HYDROLASES
• LYASES
• ISOMERASES
• LIGASES
6. OXIDOREDUCTASES
• CATALYSE OXIDATION AND REDUCTION
REACTIONS.
• They catalyse the transfer of electrons from
one molecule to the other.
• REDUCTANT= electron donor
• OXIDANT= electron acceptor
• These group of enzymes usually utilize NADP
or NAD+ .as cofactors.
• For example:- 1)OXIDASES( Poly phenyl
oxidase)
• 2)PEROXIDASE
• 3)REDUCTASES
• 4)DEHYDROGENASES
7. TRANSFERASES
• Catalyse the transfer of a specific
functional group from one
molecule to the other.
• For example:-
1)Transaminases(transfer amino
group from one molecule to
another)[ALANINE
TRANSAMINASE]
• 2)Phosphotransferases(transfer of
phosphate group)
8. HYDROLASES
• Enzymes that bring about hydrolysis of
various compounds.
• They utilize water as hydroxyl group
donor during substrate breakdown.
• For example:-1)
esterases(lipases,phosphatases)
• 2)glycosidases(sucrase,maltase)
• 3)peptidases(pepsin,trypsin)
• 4)ATPase
9. LYASES
• • Catalyze non-hydrolytic removal of functional
groups from substrates, often creating a double
bond in the product or the reverse reaction
where addition of functional group occurs at
the double bond.
• For example:-1) Decarboxylases(DOPA
Decarboxylase)
• 2)Dehydratases(ALA
Dehydratase)
• 3)Aldolases
10. ISOMERASES
• Catalyse the isomerisation
reaction(inter conversion of isomers).
• There is only one substrate yielding
one product.
• For example:-1)Racemases
• 2)Isomerases
• 3)Epimerases
11. LIGASES
• The enzyme that can catalyse the joining of two molecules
by forming a new chemical bond.
• They use energy from cleavage of ATP to form new bonds.
• For example:- DNA Ligase(form phosphoester bonds)
• Arginosuccinate synthetase(form C-N
bonds)
• Glutamine synthetase
Synthetase require ATP UNLIKE
synthase
12. Vmax
• Velocity or rate of enzyme reaction is
assessed by the rate of change of
substrate to product per unit time.
• Vmax or a maximum velocity of an
enzymatic reaction can be defined as the
rate of the reaction at which the enzyme
shows the highest turnover. Increasing
the substrate concentration indefinitely
further does not increase the rate of an
enzyme-catalyzed reaction after
reaching a certain point.
13. MICHAELIS MENTEN EQUATION
• It illustrates in mathematical
terms, the relationship between
initial reaction velocity and
substrate concentration with the
help of Michaelis constant(Km).
14. THE DEPENDANCE OF INITIAL REACTION
VELOCITY ON [S](SUBSTRATE CONCENTRATION)
AND Km CAN BE ILLUSTRATED BY EVALUATING
THE EQUATION UNDER THREE CONDITIONS:-
• 1) When [S] is much less than Km.
Means Km+[S] almost equal to Km.
• 2)When [S] is much greater than Km.
Reaction velocity is maximum hence unaffected by further increase in concentration.
• 3)When [S]=Km
Vi=Vmax/2
15. MICHAELIS CONSTANT
(Km)
• The michaelis constant Km is the
substrate concentration at which Vi is
half the maximal velocity (Vmax/2)
attainable at a particular concentration
of enzyme.
• Km hence has the dimensions of
substrate concentration.
16. SIGNIFICANCE OF Vmax
• This point is reached when there are enough
substrate molecules to completely fill the enzyme’s
active sites.
• The maximal rate(Vmax) reveals the turnover
number of an enzyme.[Turnover number= the
number of substrate molecules being catalyzed per
second]
17. SIGNIFICANCE OF Km VALUE
1. Km value is used as a measure of an enzyme’s affinity for it’s substrate.[Lower the value
of Km, higher is the enzyme’s affinity for substrate and vice versa](For example:- Km
value of glucokinase is 10mmol/L and that of hexokinase is 0.05mmol/L)
2. Determines the natural substrate of the enzyme.[ Hexokinase phosphorylates
glucose, fructose and mannose; Lowest Km value is for glucose so acts as a natural
substrate for hexokinase]
3. It gives an idea of the strength of binding of the substrate to enzyme.[Lower the
value of Km, more tightly bound is the substrate to the enzyme]
