This document discusses enzymes and coenzymes. It defines enzymes as proteins that catalyze biochemical reactions and notes they have molecular weights ranging from 10,000 to 200,000. Coenzymes are organic non-protein molecules that bind to apoenzymes to form active enzymes. There are two types of enzymes - exoenzymes act outside cells while endoenzymes act inside cells. The International Union of Biochemistry classifies enzymes into six major classes based on the type of reaction catalyzed, including oxidoreductases, transferases, hydrolases, lyases, and isomerases. Enzymes exhibit a high degree of specificity in their catalytic actions and function via the Michaelis-

1. MSCDFSMBIOCHEMISTRY
ENZYMES AND COENZYMES

2. ENZYMES :
They are the protein that catalyze biochemical reactions .louis Pasteur demonstrated the fermentation
Of glucose by yeast and the catalytic agent was called as ferment. and then the Buchner and other found
that cell free extract of yeast can ferment glucose.1926,James Summer revealed the true nature of enzyme
as he extracted the urease from jackbeans .
At present 150 different enzymes are known .
CHEMICAL NATURE OF ENZYME
ENZYME are high molecular weight compounds made up of aminoacid linked by peptide bond .they have
molecular weight from 10,000 to 2akhs .all protein are enzymes.and RNA can act as enzyme such RNA are
called ribozyme.so the ribozymes are RNA molecule with catalytic activity.these are transesterification
reaction and most are concerned with metabolism.ribosomal RNA hydrolyse aminoacyl esterand play a role
in peptide bond function.eg peptidyl transferase activity .
IMPORTANT TERMS
1. COFACTOR : molecule or ion that help in catalytic reaction
2. APOENZYME: the portion of protein that needs cofactor for reaction
3. HALOENZYME: enzyme as whole, haloenzyme consist of apoenzyme and one cofactor
4. ENZYME : the proteins that act as catalyst that speed up the reaction rate but do not alter the reaction
nature
5. COENZYME: the organic non protein molecule that bind with an apoenzyme to form active
enzyme.coenzyme are vitamins
6. ENDOENZYME: A Cell made the enzyme and it is not secreted or exported out of cel

3. 7 .SUBSTRATE : the specific molecule on which enzyme act
8 .METABOLISM : chemical reaction of cell that are under control of enzyme
9.CATABOLIC REACTION: the reaction in which chemical compounds are broken
10.ANABOLIC REACTION : reaction in which chemical compounds are synthesized
11.ENZYME IMMOBILIZATION: When an enzyme attached to a solid matrix and cannot move and act on
substrate .it is said to be immobile and process is called immobilization
12.ENZYME INACTIVATION: When an enzyme doesn’t react or participate in activity due to inhibitor or
inhibitory reactions , it is called enzyme inactivation.eg in vivo and vitro reactions.
13.ENZYME STABALIZATION: the process of reducing the inhibitory conditions so that enzyme can work
properly .
There are 2 types of enzymes :
1.Exoenzymes and 2.endoenzymes
Endoenzymes are those that act inside the cell.
Exoenzymes are those that act outside the cell.
Enzymes are proteins may have non protein component .it can be organic compound or metal . if it is
organic compound it is called coenzyme and if it is metal it is called cofactor .and the protein and non
protein part are called haloenzyme .when the non protein part tightly bound to protein it is called
prosthetic group.
When protein part dissociate from protein part ,it is called apoenzyme .

4. NOMENCLATURE AND CLASSIFICATION OF ENZYME :
Enzyme is named by addition of “ase” at the end .for eg if maltose is getting converted to glucose the
enzyme name is maltase .INTERNATIONAL UNION OF BIOCHEMISTRY(IUB) has six major classes . there
were code numbers assigned to enzyme that were prefixed by EC (Enzyme commission )
It contains 4 points separated by points.
1. The first number shows the enzyme belongs to which of 6 main classes .
2. The second figures the subclass.
3. The third figure gives the subclass
4. The forth figure is serial number of enzyme.
5. The forth digit identifies the specific enzyme. eg.alcohol :NAD oxidoreductase is given number 1.1.1.1
MAJOR CLASSES OF ENZYME AND THE TYPE OF REACTION CATALYSED
1. OXIDOREDUCTASE (EC1):they help in oxidizing and reduction reactions . eg.dehydrogenase (removal
of 2 hydrogen ) and oxidase (reduction of molecular oxygen )
2. TRANSFERASE (EC2) : transfer of group between 2 substrate ,reactions like aminotransferase that
catalyze exchange between amino and ketogroup between amino acid and keto acids .
3. HYDROLYSES(EC3) :they help in hydrolysis of substrate .peptidases that catalyze hydrolyses of peptide
bond
4. LYASES (EC4) :they help in removal of group from substrate non hydrolytically. eg,. Decarboxylase that
catalyze removal of carboxyl group from substrate.
5. ISOMERASE (EC5): help in isomerization of substrate eg. Racemases that convert D-isomer to L- isomer
and vice versa .

5. SPECIFICITY OF ENZYME: enzymes are very very specific in their action. Enzyme have 4 different type
of specificity :
1. REACTION SPECEFICITY : they catalyze only one type of reactions and act on specific substrate.eg.
Urea act on urease and catalase on hydrogen peroxide.
2. BOND SPECEFICITY :these enzyme act on specific bonds ( glyosidic ,peptide etc.) eg. Pepsin, trypsin
act on peptide bonds only .
3. GROUP SPECEFICITY : these are group specific ,they act on particular functional group .eg alcohol
dehydrogenase act on –OH group.
4. OPTICAL SPECIFICITY : they exhibit optical specificity for atleast a portion of substrate molecule .eg
Maltase catalyze the hydrolysis of α –glyosidic bond between 2 glucose molecule but not β glyosidic
bond.
MECHANISM OF ENZYME ACTION
Michaelis and Menten ,enzyme (E) first bind the substrate to form enzyme substrate complex (ES )then
it dissociate to form protein (p) and unaltered enzyme (E) .
E+S ES P+ E

6. When the substrate binds on the active site on enzyme ,the action of enzyme starts .the catalytic site of
the enzyme molecule possess a complex3d form and provides a cleft that bind substrate .ES complex is
formed by non covalent bond between group of substrate and amino acid chain present at catalytic site .
MODELS OF ES COMPLEX FORMATION
LOCK AND KEY METHOD /FISCHER MODEL
It says that catalytic site has proper conformation compatible to substrate even if the substrate is absent
.the catalytic site binds the substrate and catalyze the reaction without any change in its own
conformation .
Failures
• this model fails to explain the change of enzyme activity in presence of allosteric modulators.
Allosteric modulators are those substance when they bind on enzyme molecule other than the catalytic
site they either inhibit or enhance the activity.
• this model also fails to explain the action of non competitive inhibitors.
KOSHLAND INDUCED FIT MODEL
It says that catalytic site doesn’t have a proper conformation as explained in lock n key method . when the
substrate approaches the enzyme ,the confirmation of catalytic site change according to substrate so the
enzyme hold its substrate properly . this model very well explained the non competitive inhibition and
allosteric modulation of enzyme.
KATAL : it is the unit of enzyme activity .it is the amount of an enzyme that transforms 1mol of substrate
into product in one second.

7. IU ( international enzyme unit ) is the amount of enzyme that catalyse the transformation of 1µ mol of
substrate into product in one minute .
Specefic activity is expressed as Kat /Kg or IU /mg
Molar activity = Kat/mol
Turnover no of enzyme = number of molecule of substrate transformed per catalytic site of enzyme per
minute .