Enzymes

1. OLIGOMERIC
ENZYMES

2. What are enzymes?
Enzymes are proteins which act as catalysts
Catalyst :
A catalyst is something which by its very nature
increases the rate of a reaction and remain
uncharged at the end of reaction.

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catalyst
enzyme

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Enzymes control and regulate the
various metabolic activities inside
living cells.

6. The definition of enzymes?
Enzymes are powerful and highly effectual
biocatalyst produced by living tissues which
increase the rate of reactions that occur in the
tissue.

7. What are enzymes made up of ?
Almost all enzymes are make up of proteins

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monomeric sarcosineoxidase
Monomeric enzymes
Monomeric enzymes only contains tertiary structure
trypsin

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Chymotypsin and trypsin

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Oligomeric enzyme
Oligomeric enzymes
contains two or more polypeptide chains associated by
noncovalent forces.

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Zymogen
Several enzymes are produced and stored as
inactive precursors called zymogens
Isozymes
Enzymes which catalyze the same reaction but
have different primary and quaternary structure.
The most common isozymes are polymeric
enzymes.
May have similar but not identical amino acid
sequences.
May have common evolutionary origin.

16. Oligomeric enzymes consist of two or more
polypeptide chains which are usually linked to
each other by non covalent interactions and
never by peptide bonds. The component
polypeptide chains are termed sub-units and
may be identical ,they are some times called
protomers. Dimeric proteins consist of
two,trimeric proteins of three and tetrameric
proteins of four sub-units. The molecular
weight is usually in excess of 35000.

17. The vast majority of known enzymes are
oligomeric for example ,all of the enzymes
involved in glycolysis process either two or four
sub-units. It is therefore, reasonable to assume
that the sub-units of oligomeric proteins in
association that they do not have in isolation.
such enzymes are not synthesized as inactive
zymogens, but their activities may be regulated
in a far more precise way by feed-back
inhibition. This is possible because many
oligomeric proteins exhibit allostery their
different binding sites interact.

18. LACTATE DEHYDROGENSE
Vertebrate LDH is an ex of oligomeric enzyme
where each subunit has the same function ,in this
case to catalise the reaction
CH3.CH.CO2־ + NAD+ CH3.C=O.CO2־
| || PYRUVATE

OH O

(S)-LACTATE + NADH + H+

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 e.g. LDH(lactate dehydrogenase) LDH
1,2,3,4,5 are HHHH, HHHM, HHMM,
HMMM and MMMM . i.e. LDH isozymes
are tetramers formed by 2 sets of subunits.

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Significance :
 In the heart, LDH1 (4 H) H=heart, catalyzes Lactate
convert to pyruvate for energy supply
 In muscles, LDH5 ( 4M ) M=muscle, convert pyr to
Lact. For energy storage
 Clinical diagnosis using isozyme. E.g. when heart
attack(infarction) happens, enzymes release from
injured cells to the blood showed different
enzyme(isozyme ) pattern.
 Isozyme pattern: different isozymes appear as a
peak sooner or later followed by the progress of the
disease.

23. LACTSOSE SYNTHASE
• Mammary gland lactose synthase is an example
of oligomeric enzyme where a non functional sub
unit modifies the behavior of a functional sub
unit. This enzyme as isolated from milk , consist
of two subunits: one of these catalytically
inactive protein , α-lactalbumin , found only in
mammary gland; the other is N-acetyl
lactosaminesynthase, an enzyme present in most
tissues .
•is N-acetyl lactosaminesynthase, in the absence
of α-lactalbumin, catalyses the reaction

24. This is important in the synthesis of the carbohydrate
components of glycoprotein's, the enzyme is also
produced and stored in the mammary gland during
pregnancy ,when levels of α-lactalbumin are low. After the
birth of the baby, reduced synthesis of the hormone
progesterone in the mother leads to increased synthesis
of the luteotrophic hormone (prolactin), stimulating the
production of alpha lactalbumin in the mammary gland.
This combines with the stored is N-acetyl lactosamine
synthase to form lactose synthase an enzyme which
speculates production of the lactose components lactose
synthase, an enzyme with facilitates the production of the
lactose components of the milk required for the newborn
baby. Lactose synthase catalyses the reaction:
UDP-galactose + glucose UDP + lactose

25. TRYPTOPHAN SYNTHASE
• Tryptophan synthase of E.coli is an ex of oligomeric
enzyme which contains two different functional sub-
units the enzyme catalyses the reaction
•Indole-3-glyserolphasphate+L-serine

• L-tryptophan+glyceraldehyde-3-phosphate
•It can be dissociated into two or further units, each of
molecular weight 29000 and a beta-2 subunit, of
molecular weight 90000, the beta-2 subunit further
dissociates the presence of 4 M urea to give two beta
subunits, each of which has a binding site for the co-
enzyme pyrodoxal phosphate.
•The isolated alpha-subunit will catalyze the reaction:
•Indole-3-glyserolphasphate indole + glyceraldehyde-3-
phosphate.
•The isolated beta-subunit also has catalytic activity but
for the reaction:
•Indole + L-serine L- tryptophan.
Pyridoxal phosphate
Pyridoxal phosphate

26. PYRUVATE DEHYDROGENASE
•The same type of organization as tryptophan
synthase, but on an even larger scale. The
Enzyme Commission recommended that such a
complex should be regarded as a system of
separate enzymes rather than as single enzyme.

•Pyruvate dehydrogenase enables pyruvate to
enter the TCA Cycle by, catalyzing its overall
conversion to acetyl-coA:
•Pyruvate + Co ASH + NAD+ acetyl– CoA +
• CO2 + NADH.

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several factors contribute to enzyme catalysis
2. Electrostatic effects
3. Acid-base catalysis
4. Covalent Catalysis
1. Proximity effects and orientation
arrange:

28. THANK YOU…