ENZYMES
1
History of Enzymes
-1700s and early 1800s,
the digestion of meat by
stomach secretions and the
conversion of starch to
sugars by plant extracts
and saliva were known.
--mechanism by which this
occurred had not been
identified.
2
History of Enzymes
-19th century, when studying the fermentation of
sugar to alcohol by yeast, Louis Pasteur came to
the conclusion that it was catalyzed by a vital
force contained within the yeast cells called
"ferments", which were thought to function only
within living organisms.
--He wrote that "alcoholic fermentation is an act
correlated with the life and organization of the
yeast cells, not with the death or putrefaction of
the cells.
Yeast
3
History of Enzymes
 1878: German physiologist Wilhelm Kühne
 first used the term enzyme, which literally means “in
yeast”
 1897: Eduard Buchner
 began to study the ability of yeast extracts that lacked
any living yeast cells to ferment sugar. He also found that
the sugar was fermented even when there were no living
yeast cells in the mixture.
 He named the enzyme that brought about the
fermentation of sucrose "zymase". In 1907 he received
the Nobel Prize in Chemistry “for his biochemical
research and his discovery of cell-free fermentation".
4
Enzymes
 Enzymes are biomolecules that
catalyze, increase the rates of
chemical reactions without being
altered during the reaction.


Almost all enzymes are proteins;
Enzymes are essential to life.
 In enzymatic reactions, the
molecules at the beginning of the
process are called substrates, and
the enzyme converts them into
different molecules, the products.
5
Enzymes
 Almost all processes in a
biological cell need enzymes in
order to occur at significant
rates.
 Since enzymes are extremely
selective for their substrates and
speed up only a few reactions
from among many possibilities,
the set of enzymes made in a cell
determines which metabolic
pathways occur in that cell.
6
Enzymes
 Enzyme activity can be
affected by other molecules.


Inhibitors are molecules
that decrease enzyme
activity.
Inducers are molecules that
increase activity. Many
drugs and poisons are
enzyme inhibitors.
 Activity is also affected by
temperature, chemical
environment (e.g. pH),
7
Enzyme Inhibitor & Inducer
Enzyme Inhibitor
Enzyme Inducer
Cimetidine
Ketoconazole
Fluconazole
Miconazole
Macrolides(except
Azithromycin)
Fluoroquinolones(except
Levofloxacin)
Rifampicin
Carbamazepine
Phenobarbital
Phenytoin
Griseofulvin
Smoking
Chronic alcoholism
8
ENZYMES are biological
catalyst
ENZYME CHARACTERISTICS
1. The basic function of an enzyme is to
increase the rate of a reaction
2. Most enzymes act specifically with only one
reactant (called a substrate) to produce
products
3. The most remarkable characteristic is that
enzymes are regulated from a state of low
activity to high activity and vice versa
9
Enzymes Lower a Reaction’s
Activation Energy
10
Enzyme Action
11
Three-dimensional structure of
an ENZYME
12
Three-dimensional structure of
an ENZYME
 Enzymes are
proteins
 They have a
globular shape
 A complex 3-D
structure
Human pancreatic amylase
13
Enzyme Structure
 Most enzymes are proteins
 Enzymes may require a non-peptide component
as a cofactor. The peptide component is called
the apoenzyme, the cofactor is called as the
coenzyme and the combined functional unit is the
holoenzyme
 Cofactors that are tightly bound to the
polypeptide are called prosthetic groups. Such
proteins are called as complex or conjugated
proteins. Proteins without prosthetic groups are
simple proteins
14
The Active Site
 One part of an enzyme,
the active site, is
particularly important
 The shape and the
chemical environment
inside the active site
permits a chemical
reaction to proceed
more easily
15
 May be inactive in its
APOENZYME
original synthesized
structure
PROENZYME
OR ZYMOGEN
 The inactive form of
the apoenzyme
 May contain several
extra amino acids in
the protein which are
removed, and allows
the final specific
tertiary structure to be
formed before it is
activated as an
apoenzyme
16
The Substrate
 The substrate of an enzyme are the reactants
that are activated by the enzyme;
 Enzymes are specific to their substrates;
 The specificity is determined by the active site.
17
COFACTOR
 An additional non-
protein molecule that is
needed by some
enzymes to help the
reaction
Nitrogenase enzyme with Fe, Mo and ADP
18
cofactors
COFACTOR
 A non-protein substance
which may be organic
and called coenzyme
 Common coenzymes are
vitamins and metal ions
19
COFACTOR
 Another type of cofactor is an inorganic metal
ion called a metal


ion activator
Are inorganic and may be bonded through
coordinate covalent bonds
Metal ions as Zn+2, Mg+2, Mn+2, Fe+2, Cu+2, K+,
and Na+1 are used in enzymes as cofactors
20
21
Vitamins as Coenzymes
Vitamin
Niacin
Riboflavin
Pantothenic acid
Vitamin B12
Thiamine (B1)
Coenzyme
nicotinamide adenine
dinucleotide (NAD+)
flavin adenine
dinucleotide (FAD)
coenzyme A (CoA)
coenzyme B-12
thiaminpyrophosphate
(TPP)
Function
oxidation or
hydrogen transfer
oxidation or
hydrogen transfer
Acetyl group carrier
Methyl group
transfer
Aldehyde group
transfer 22
PROSTHETIC GROUPS
 Are tightly incorporated into protein structure by
covalent or noncovalent forces
 Examples include derivatives of B vitamins
such as pyridoxal phosphate, flavin
mononucleotide (FMN), flavin adenine
dinucleotide (FAD), thiamin pyrophosphate,
biotin and METAL IONS of Co, Cu, Mg, Mn,
and Zn.
 METALLOENZYMES – enzymes that contain
tightly bound metal ions
23
PROSTHETIC GROUPS
24
NOMENCLATURE
 The commonly used names for most
enzymes describe the type of reaction
catalyzed, followed by the suffix –ase.
Dehydrogenases – remove hydrogen atoms
 Proteases – hydrolyze proteins
 Isomerases – catalyze rearrangement in
configuration

25
NOMENCLATURE
 Modifiers may precede the name to indicate;
(a) the substrate (xanthine oxidase)
(b) the source of the enzyme (pancreatic
ribonuclease)
(c) its regulation (hormone-sensitive lipase)
(d) a feature of its mechanism of action (cysteine
protease)
26
NOMENCLATURE
 Alphanumeric designators may be added to
identify multiple forms of an enzyme ( eg., RNA
polymerase III; protein kinase C )
 Some enzymes retain their original trivial names,
which give no hint of the associated enzymatic
reaction

Examples are pepsin, trypsin, and chymotrypsin
which catalyzes the hydrolysis of proteins
27
28
Classification of Enzymes
Based on catalyzed reactions, the nomenclature
committee of the International Union of
Biochemistry and Molecular Biology
(IUBMB) recommended the following classification:
1. OXIDOREDUCTASES


Catalyze a variety of oxidation-reduction
reactions
Common names include dehydrogenase,
oxidase, reductase and catalase
29
Classification of Enzymes
2. TRANSFERASES



Catalyze transfers of groups
(acetyl, methyl, phosphate,
etc.).
The first three subclasses
play major roles in the
regulation of cellular
processes.
The polymerase is essential
for the synthesis of DNA
and RNA.
30
Three major regulatory chemical reactions. (a) Acetylation - addition of an acetyl group to
lysine's R group by acetyltransferase. (b) Methylation - addition of a methyl group to DNA's
base (e.g. cytosine) by methylase. (c) Phosphorylation - addition of a phosphate group to the R
group of tyrosine, serine or threonine (only tyrosine is shown here) by protein kinase.31
Classification of Enzymes
3. HYDROLASES
Catalyze hydrolysis reactions where a molecule is
split into two or more smaller molecules by the addition
of water
 PROTEASES split protein molecules


HIV protease is essential for HIV replication
Caspase plays a major role in apoptosis
 NUCLEASES split nucleic acids (DNA and RNA)
 Based on the substrate type, they are divided into RNase
and DNase.


RNase catalyzes the hydrolysis of RNA
DNase acts on DNA
32
Classification of Enzymes
 Nucleases cont…
 They may also be divided into exonuclease and
endonuclease.


The exonuclease progressively splits off single
nucleotides from one end of DNA or RNA.
The endonuclease splits DNA or RNA at internal sites.
 PHOSPHATASE catalyzes dephosphorylation
(removal of phosphate groups).


Example: calcineurin (also known as protein
phosphatase 3)
The immunosuppressive drugs Tacrolimus,
Sirolimus, Everolimus and Cyclosporin A are the
calcineurin inhibitors
33
Classification of Enzymes
4. LYASES
 Catalyze the cleavage of
C-C, C-O, C-S and C-N
bonds by means other
than hydrolysis or
oxidation.
 Common names include
decarboxylase and
aldolase.
5. ISOMERASES
 Catalyze atomic
rearrangements within a
molecule.
 Examples include
rotamase, protein
disulfide isomerase (PDI),
epimerase and racemase
34
The role of rotamase and protein disulfide
isomerase (PDI). The reactions catalyzed by
the two enzymes can assist a peptide chain to
fold into a correct three-dimensional structure
35
6. LIGASES
 Catalyze the reaction which joins two molecules
 Examples include peptide synthase, aminoacyl-
tRNA synthetase, DNA ligase and RNA ligase
The IUBMB committee also defines subclasses
and sub-subclasses
 Each enzyme is assigned an EC (Enzyme Commission) number
For example, the EC number of catalase is EC1.11.1.6
The first digit indicates that the enzyme belongs to oxidoreductase
(class 1)
Subsequent digits represent subclasses (1.11. acting on a peroxide
as acceptor) and sub-subclasses (1.11.1peroxidases)
36
Mechanism of Enzyme Action
The molecule acted upon
a unique geometric shape
that is complementary to
the geometric shape of a
substrate molecule
37
Mechanism of Enzyme Action
38
Mechanism of Enzyme Action
Lock and Key Theory
 first postulated in 1894
by Emil Fischer
 The lock is the enzyme
and the key is the
substrate
 Only the correctly sized
key (substrate) fits into
the key hole (active site)
of the lock (enzyme)
39
The Lock and Key
Hypothesis
S
E
E
E
Enzymesubstrate
complex
Enzyme may
be used again
P
P
Reaction coordinate
40
The Induced Fit Theory
 Postulated by Daniel
Koshland
 It states that, when
substrates approach and
bind to an enzyme they
induce a conformational
change
 This change is analogous
to placing a hand
(substrate) into a glove
(enzyme)
41
The Induced Fit Theory
 Some proteins can change their shape
(conformation)
 When a substrate combines with an enzyme, it
induces a change in the enzyme’s conformation
 The active site is then moulded into a precise
conformation
 Making the chemical environment suitable for the
reaction
 The bonds of the substrate are stretched to make
the reaction easier (lowers activation energy)
42
The Induced Fit Theory
 This explains the enzymes that can react with a
range of substrates of similar types
Hexokinase (a) without (b) with glucose substrate
http://www.biochem.arizona.edu/classes/bioc462/462a/NOTES/ENZYMES/enzyme_mechanism
.html
43
The Induced Fit Theory
 Assumes that the substrate plays a role in determining the
final shape of the enzyme and that the enzyme is
partially flexible.
 This explains why certain compounds can bind to the
enzyme but do not react because the enzyme has been
distorted too much
 Other molecules may be too small to induce the proper
alignment and therefore cannot react
 Only the proper substrate is capable of inducing the
proper alignment of the active site
44
This is a molecular model of
the unbound carboxypeptidase
A enzyme
This is a representation of
carboxypeptidase A with a substrate
(turquoise) bound in the active site. The
active site is in the induced
45
conformation.
MECHANISMS TO FACILITATE
CATALYSIS
A. CATALYSIS BY PROXIMITY
 For molecules to react, they must come within bondforming distance of one another
 The higher the concentration, the more frequently
they will encounter one another and the greater will be
their rate of interaction
 aka entropy reduction
 ACID-BASE CATALYSIS
 Can be specific or general
 “Specific” meaning only protons (H3O+ , specific acid)
or OH- ions (specific base)
46
MECHANISMS TO FACILITATE
CATALYSIS
 Proximity: Reaction between bound molecules
doesn't require an improbable collision of 2
molecules -- they're already in "contact"
(increases the local concentration of reactants).
 Orientation: Reactants are not only near each
other on enzyme, they're oriented in optimal
position to react, so the improbability of colliding
in correct orientation is taken care of.
47
Rate enhancement by
entropy reduction.
a) bimolecular reaction (high activation
energy, low rate)
48
Rate enhancement by
entropy reduction.
 b) unimolecular reaction, rate enhanced by
factor of 105 due to increased probability of
collision/reaction of the 2 groups.
49
Rate enhancement by
entropy reduction.
 c) constraint of structure to orient groups better
(elimination of freedom of rotation around bonds
between reactive groups), rate enhanced
by another factor of 103, for 108 total rate
enhancement over bimolecular reaction.
50
MECHANISMS TO FACILITATE
CATALYSIS
 When substrate binds to enzyme, water is usually
excluded from active site (desolvation).
 causes local dielectric constant to be lower,
which enhances electrostatic interactions in the
active site, and also
 results in protection of reactive groups from water,
so water doesn't react to form unwanted biproducts.

Of course, if water is a substrate, it has to be "allowed in", but
maybe only in a certain sub-part of active site.
 Involvement of charged enzyme functional groups in
stabilizing otherwise unstable intermediates in the
chemical mechanism can also correctly be called
"electrostatic catalysis".
51
MECHANISMS TO FACILITATE
CATALYSIS
 CATALYSIS BY STRAIN


Strain is created by binding to substrates in a conformation
slightly unfavorable for the bond to undergo cleavage
The strain stretches or distorts the targeted bond,
weakening it and making it more vulnerable to cleavage
 probably the most important rate enhancing
mechanism available to enzymes
 Enzyme binds transition state of the reaction more
tightly than either the substrate or product -therefore DG‡ is reduced, and rate is enhanced.
52
Strain
 "Strain" is a classic concept in which it was supposed that
binding of the substrate to the enzyme somehow caused
the substrate to become distorted toward the transition
state. It's unlikely that there is enough energy available in
substrate binding to actually distort the substrate toward
the transition state.
 It's possible that the substrate and enzyme interact
unfavorably and this unfavorable interaction is relieved in
the transition state.
 It's more likely that the enzyme is strained, as for
example in induced fit.
53
MECHANISMS TO FACILITATE
CATALYSIS
 Transition state stabilization is a more modern concept:
it is not the substrate that is distorted but rather that the
transition state makes better contacts with the enzyme
than the substrate does, so the full binding energy is not
achieved until the transition state is reached.
 Induced fit assumes that the active site of an enzyme is
not complementary to that of the transition state in the
absence of the substrate. Such enzymes will have a lower
value of kcat/Km, because some of the binding energy must
be used to support the conformational change in the
enzyme. Induced fit increases Km without increasing kcat.
54
MECHANISMS TO FACILITATE
CATALYSIS
 COVALENT CATALYSIS



Involves the formation of a covalent bond between
the enzyme and one or more substrates
Introduces a new reaction pathway with lower
activation energy thus faster than the reaction
pathway in homogenous solution
Common among enzymes that catalyze group
transfer reactions
55
ENZYME KINETICS
The field of biochemistry concerned
with the quantitative measurement of
the rates of enzyme-catalyzed
reactions and the systematic study of
factors that affect these rates
56
ENZYME KINETICS
REACTION MODEL
where
S is the substrate
E is the enzyme
ES is the enzyme-substrate complex
k1, k-1, and k2 are rate constants
57
MICHAELIS MENTEN
EQUATION
Describes how reaction velocity varies
with substrate concentration
vo =
Vmax S
Km + S
whereVo = initial reaction velocity
Vmax = maximal velocity
Km = Michaelis constant (k-1 + k2)/k1
S= substrate concentration
58
ASSUMPTIONS
1. Relative concentrations
of E and S
–
S >E, so [ES] at any time is small
2. Steady-state assumption
–
–
[ES] does not change in time
E + S = ES = E + P, the rate of formation of ES is equal
to that of the breakdown of ES
3. Initial velocity
–
–
–
Used in the analysis of enzyme reactions
Rate of reaction is measured as soon as E and S are
mixed
P is very small, the rate of back reaction from P to S
can be ignored
59
CONCLUSIONS
1. Characteristics of Km
a. Small Km
reflects high affinity of the E for S
because a low concentration of S is
needed to half-saturate the enzyme –
that is, reach a velocity that is ½ Vmax
b. Large Km
Reflects low affinity of E for S because
a high concentration of S is needed to
half-saturate the enzyme
60
Effect of substrate concentration
on reaction velocities
Small Km for enzyme
1 reflects a high
affinity of enzyme for
the substrate
Large Km for enzyme
2 reflects low affinity
of enzyme for the
substrate
61
CONCLUSIONS
2. Relationship of velocity to enzyme concentration
The rate of reaction is directly proportional to the
enzyme concentration at all substrate
concentrations
3. Order of reaction
First order - S < Km, the velocity of reaction is
roughly proportional to the enzyme concentration
Zero order - S > Km, the velocity is constant and
equal to Vmax; the rate of reaction is then
independent of substrate concentration
62
At high concentration of
substrate( [S]>>Km), The
At of the reaction is
velocity
zero order – that is, constant
and independent OF
substrate concentration
At low concentration of
substrate( [S]<<Km), The
velocity of the reaction is first
order – that is, proportional
to substrate concentration
63
Lineweaver-Burk Plot
Also called a doublereciprocal plot
If 1/v0 is plotted VS 1/[S], a
straight line is obtained
The intercept on the x-axis is
equal to -1/Km
The intercept on the y-axis is
equal to 1/Vmax
64
Lineweaver-Burk Plot
Can be used to calculate Km and Vmax as well
as to determine the mechanism of enzyme
inhibitors
Equation describing the Lineweaver-Burk
Plot is:
65
INHIBITION OF ENZYME
ACTIVITY

INHIBITOR – substance that can diminish
the velocity of an enzyme catalyzed reaction
TYPES OF INHIBITION:
1. COMPETITIVE INHIBITION
2. NONCOMPETITIVE INHIBITION
66
COMPETITIVE INHIBITION


Inhibitor binds
reversibly to the same
site that the substrate
would normally occupy,
and therefore competes
with the substrate for
that site
Inhibitors tend to
resemble the structures
of a substrate, and thus
are termed as substrate
analogs
67
COMPETITIVE INHIBITION

Succinate
SDH
Malonate

SDH
Malonate
(¯OCOCH2COO¯)
competes with Succinate
(¯OOCCH2CH2COO¯)
for the active site of succinate
dehydrogenase (SDH)
SDH catalyze the removal of
one H atom from each of the
2 methylene C’s of succinate
68
-2H
Succinate
Fumarate
(¯OOC-CH2-CH2-COO¯)
(¯OOC-HC=CH-COO¯)
Malonate – Enzyme Complex
NO REACTION
69
Consequences of competitive
inhibition


Vmax is unchanged: At
high levels of substrate
all of the inhibitor is
displaced by substrate.
Km is increased:
Higher substrate
concentrations are
required to reach the
maximal velocity.
70
NONCOMPETITIVE INHIBITION



Inhibitor and substrate
bind at different sites
on the enzyme
The inhibitor binds to
both E and ES
The noncompetitive
inhibitor binds to an
allosteric site
(different location than
the active site) of an
enzyme

The binding of an
inhibitor to the allosteric
site alters the shape of the
enzyme, resulting in a
distorted active site that
does not function
properly.
71
Effect of Enzyme inhibition on
Lineweaver-Burk plot
72
NONCOMPETITIVE INHIBITION


Vmax is decreased: At
high levels of
substrate the inhibitor
is still bound.
Km is not changed:
Noncompetitive
inhibitors do not
interfere the binding
of substrate to
enzyme
73
74
FACTORS AFFECTING ENZYME
REACTIONS
I. SUBSTRATE CONCENTRATION
• The rate of enzyme
catalyzed reaction
increases with substrate
concentration until a
maximal velocity (Vmax)
is reached
75
Effect of Temperature

The rate of enzymecatalysed reactions
increases as the
temperature rises to the
optimum temperature

Enzymes are usually damaged
above about 45°C
Above a certain
temperature, activity
begins to decline because
the enzyme begins to
denature
76
Effect of pH





Each enzyme has an optimal
pH
In order to interact, the E
and S have specific chemical
groups in ionized or
unionized state
Amino group in protonated
form (-NH3+)  increase
catalytic activity
At alkaline pH, amino group
is deprotonated  decrease
in rate of reaction
Extremes of pH can lead to
denaturation
77
REGULATION OF
ENZYME ACTIVITY
A. ALLOSTERIC REGULATION
B. REGULATION OF ENZYMES
BY COVALENT MODIFICATION
78
A. ALLOSTERIC REGULATION

EFFECTORS – molecules that regulate
allosteric enzymes that bind noncovalently at
a site other than the active site


Negative effectors – inhibit enzyme activity
Positive effectors – increases enzyme activity
79
HOMOTROPIC EFFECTORS



Substrate itself serves as an effector
Most often a positive effector
The presence of a substrate molecules at one
site on the enzyme enhances the catalytic
properties of the other substrate-binding
sites(their sites exhibit cooperativity)
80
HETEROTROPIC EFFECTORS

The effector may be different from the substrate
81
Feedback Inhibition
82
B. REGULATION OF ENZYMES BY
COVALENT MODIFICATION

Most frequently by the addition or removal of
phosphate group from specific Ser, Thr, and Tyr
residues of the enzyme
ATP
ADP
Protein
kinase
Enzyme-OH
Enzyme-OPO3=
Protein
phosphatase
HPO4=
H2O
83
Response of Enzyme to
phosphorylation


Phosphorylated form may be more or less active
than the unphosphorylated enzyme
Glycogen phosphorylase (degrades glycogen)
activity is increased


low activity (E), high activity (EP)
Glycogen synthase (synthesize glycogen) activity
is decreased

low activity (EP), high activity (E)
84
INDUCTION and REPRESSION
of enzyme synthesis



Alter the total population of active sites rather
than influencing the efficiency of existing enzyme
molecules
Enzymes that are needed at only one stage of
development or under selected physiologic conditions
are subject to regulation of synthesis
Enzymes that are in constant use are NOT
regulated by altering the rate of enzyme synthesis
85
Mechanisms for Regulating
Enzyme Activity
Regulator
event
Typical
effector
Results
Time
required for
change
Substrate
Availability
Substrate
Change in
velocity
Immediately
Product
inhibition
Product
Change in Vmax
and/or Km
Immediately
Allosteric
control
End product
Change in Vmax
and/or Km
Immediately
Another enzyme Change in Vmax
and/or Km
Immediately minutes
Covalent
modification
Synthesis or
degradation of
enzyme
Hormone or
metabolite
Change in the
amount of
enzyme
Hours to days
86
Enzyme Activity is
Often Regulated
Feedback inhibition a common form of
enzyme regulation in
which the product
inhibits the enzyme .
87
88
Enzymes - Activity

Temperature and pH effect enzyme action
89
Enzymes - Activity

Temperature and pH effect enzyme action
90
Enzymes - Activity

Enzyme and substrate concentrations
91
92
ENZYMES IN
CLINICAL USE
Enzyme inhibitors as DRUGS
Enzymes in CLINICAL
DIAGNOSIS
93
Enzyme inhibitors as DRUGS
1.
2.
3.
4.
STATINS – HMG Coenzyme A reductase inhibitors;
lower serum lipid concentration
EMTRICTABINE and TENOFOVIR DISOPROXIL
FUMARATE – inhibitors of viral reverse
transcriptase; block replication of HIV
ACE Inhibitors (Captopril, Lisinopril, Enalapril) –
antihypertensive agents
Lactam Antibiotics (Penicillin and Amoxicillin) –
inhibitors of alanyl alanine carboxypeptidasetranspeptidase, thus blocking cell wall synthesis
94
Enzymes in CLINICAL DIAGNOSIS
2 GROUPS OF PLASMA ENZYMES
(1) Actively secreted into the plasma by certain
organs
(2) Released from the cells during normal cell
turnover


Intracellular, have no physiologic function in the
plasma
Constant level in healthy individuals and represent a
steady state
95
Elevated enzyme activity in the plasma may
indicate tissue damage accompanied by
increased release of intracellular enzymes,
thus useful as a diagnostic tool
Elevated levels of
ALT (alanine
aminotransferase;
also called
glutamate: pyruvate
transaminase; GPT)
signals damage
96
ISOENZYMES




Also called isozymes
Enzymes that catalyze the same reaction but
differ in their physical properties because of
genetically determined differences in amino acid
sequence
Different organs frequently contain characteristic
proportions of different isoenzymes
Isoenzymes found in the plasma serve as a means
of identifying the site of tissue damage
97
CK, Creatinine kinase





also called Creatinine phosphokinase (CPK)
3 isoenzymes; CK1, CK2, and CK3
Each isoenzyme is a dimer composed of 2
polypeptides (B and M subunits: CK1=BB,
CK2=MB, CK3=MM)
CK2(MB) isoenzyme is present in more than 5% in
myocardial muscles
Appears approximately 4 to 8 hours following onset
of chest pain, and reaches a peak in activity at
approximately 24 hours
98
LACTATE DEHYDROGENASE
(LDH)


Elevated following an infarction peaking 3 to 6
days after the onset of symptoms
Of diagnostic value in patients admitted more
than 48 hours after the infarction
99
Principal Serum Enzymes Used in Clinical
Diagnosis
Serum Enzyme
Aminotransferases
Aspartate aminotransferase
(AST, or SGOT)
Alanine aminotransferase
(ALT, or SGPT)
Major Diagnostic Use
Myocardial infarction
Viral hepatitis
Amylase
Acute pancreatitis
Ceruplasmin
Hepatolenticular degeneration
(Wilson’s disease)
Creatinine kinase
Muscle disorders and
myocardial infarction
100
Principal Serum Enzymes Used in Clinical
Diagnosis
Serum Enzyme
Major Diagnostic Use
-Glutamyl transpeptidase
Various liver diseases
Lactate dehydrogenase
(isoenzymes)
Lipase
Myocardial infarction
Phosphatase, acid
Metastatic carcinoma of the
prostate
Phosphatase, alkaline
Various bone disorders,
obstructive liver diseases
Acute pancreatitis
101