Enzymes as diagnostic &
therapeutic tool
Prepared by: Shaikh Abusufyan
Objectives
• List the clinically important
isoenzymes.
enzymes and
• State which enzymes and isoenzymes are found
in which tissues
• Use of enzymes as diagnostic & therapeutic tool
Enzymes
Biological catalysis
Very efficient –can increase reaction rates
at the order of x 10
All are proteins- so liable to denaturation
Specific to substrates
Partly specific to tissues
Measurement of serum enzymes

Diagnostic enzymology

Enzymes are normally intracellular and LOW concentration
in blood

Enzyme release (leakage)in the blood indicates cell damage
(cell –death, hypoxia, intracellular toxicity)

Quantitative measure of cell/tissue damage

Fairly non invasive possible to do repeated tests

Organ specificity- but not absolute specificity
Information from enzymes
measurements in serum
 Presence
 Organs
of disease
involved
 Aetiology
/nature of disease: differential
diagnosis
 Extent
of disease-more damaged cells-more
leaked enzymes in blood
 Time
course of disease
Enzymes routinely measured
NAME OF THE ENZYME
PRESENT IN
Aspartate Amino transferase (AST)
Serum glutamate-oxaloacetate
transaminase (SGOT)
Heart and Liver
Alanine Amino transferase (ALT)
Serum glutamate-pyruvate transaminase
(SGPT)
Heart and Liver
Alkaline Phosphatase (ALP)
Bone, intestine and other tissues
Acid Phosphatase (ACP)
Prostate
 glutamyl Transferase ( GT)
Liver
Measurement of enzyme activity
• Enzyme activity is expressed in International
unit (IU)
It corresponds to the amount of enzymes that
catalyzes the conversion of one micromole
(mol) of substrate to product per minute
LACTATE DEHYDROGENASE (LDH)
Pyruvate
Lactate (anaerobic glycolysis)
 LDH is elevated in myocardial infarction, blood disorders
 It is a tetrameric protein and made of two types of
subunits namely H = Heart, M = skeletal muscle
 It exists as 5 different isoenzymes with various
combinations of H and M subunits
Isoenzyme Composition Composition
name
Present in
Elevated in
LDH1
( H 4)
HHHH
Myocardium,
RBC
myocardial
infarction
LDH2
(H3M1)
HHHM
Myocardium,
RBC
LDH3
(H2M2)
HHMM
Kidney,
Skeletal
muscle
LDH4
(H1M3)
HMMM
Kidney,
Skeletal
muscle
LDH5
(M4)
MMMM
Skeletal
muscle, Liver
Skeletal muscle
and liver
diseases
CREATINE KINASE (CK)
Creatine + ATP
phosphocreatine + ADP
(Phosphocreatine – serves as energy reserve during muscle
contraction)
 Creatine kinase is a dimer made of 2 monomers
 Skeletal muscle contains M subunit, Brain
contains B subunits
 Three different isoenzymes are formed
Isoenzyme Composition Present in
name
Elevated in
CK-1
CNS diseases
CK-2
CK-3
BB
Brain
MB
Myocardium Acute
myocardial
/ Heart
infarction
MM
Skeletal
muscle,
Myocardium
ALANINE TRANSAMINASE (ALT) or SGPT
AND ASPARTATE TRANSAMINASE( AST) or SGOT
Alanine
transaminase
transaminase
(AST)
(ALT)
enzymes
and
are
Aspartate
the
most
abundantly present in the liver
Elevated
in blood as a result of leakage from damaged
cells
Measurement
of these transaminases is useful for the
diagnosis of liver diseases
ALANINE TRANSAMINASE (ALT) AND
ASPARTATE TRANSAMINASE ( AST).......
●
●
●
In viral hepatitis the enzyme levels are increased
20-50 times
Alanine transaminase (ALT) increase is specific
for liver damage involving hepatocellular damage
Aspartate transaminase (AST) is moderately
increased in Muscular dystrophy and acute
myocardial infarction
ENZYMES AS A DRUG TARGET
Renin
Renin:
●
Enzyme released by Juxtaglomerular cells of the
kidney
●
Maintain the BP.
●
Role-
Conversion of angiotensinogen to
angiotensin- I
ACE
ACE:
Enzyme relesed by Adrenal cortex of the kidney
●
Role:
Conversion of angiotensin- I to angiotensin- II
Increases the BP
Renin- agiotensin system
Monoamine oxidase (MAO)
●
●
It is a membrane-bound mitochondrial enzyme that oxidatively
deaminates primary amines to aldehydes.
Location:
- liver, kidney, intestine and nervous tissue
●
-
Substrates:
Catecholamines (dopamine, noradrenaline and adrenaline),
tyramine, phenylephrine and tryptophan derivatives (5hydroxytryptamine and tryptamine).
There are 2 type of MAO
1. MAO-A
- It oxidise mainly NA & 5-HT
- Inhibited selectively by v low concentration of
chlorgyline & moclobemide (Antidepressant).
MAO-B:
- It oxidizes DA in the brain
- selectively inhibited by selegiline (Antiparkinson).
●
Liver contain equal amount of both MAO enzyme
while brain contain MAO- B.
cholinesterase
2 main types of cholinesterase r
1. Acetylcholinesterase (AchE) or true
cholinesterase
2. Butyrocholinesterase (BuChE) or
Pseudocholinesterase
Responsible for degradation of Ach
1.Acetylcholinesterase
cholinesterase
(AchE)
or
Location:
- Neurone, ganglia and myoneural junction.
Function:
- Rapidly hydrolyzes acetylcholine
true
2. Butyrocholinesterase (BuChE) or
Pseudocholinesterase
Location:
Plasma, RBCs, liver, glia and other organs
Function:
- hydrolysis of Ach slowly
HMG CoA reductase
-
It is the rate-limiting enzyme in cholesterol
biosynthesis.
- Statins inhibit this enzyme, lowering cytoplasmic
cholesterol.
- And used in the treatment of Hyperlipedemia
Cyclo-oxygenase (COX)
There are two main isoforms, COX-1 and COX-2.
- COX-1 is a constitutive enzyme which is present in
platelets and other cells.
- COX-2 is an inducible form, which is produced in
response to cytokine stimulation in areas of
inflammation.
- Produces large amounts of prostaglandins &
responsible for inflammation.
Cyclo-oxygenase (COX)...
- CoX inhibitores are used as antiinflammatory
- Eg: Diclofenac, Cilicoxif ect
lanosterol 14-α-demethylase
- It is a fungal cytochrome-haem P450 enzyme,
- Responsible for synthesise of ergosterol from lanosterole.
Inhibition of enzyme
disrupts the acyl chains of fungal membrane phospholipids,
increasing membrane fluidity and causes membrane leakage
and dysfunction of membrane-bound enzymes
lanosterol 14-α-demethylase
- lanosterol 14-α-demethylase inhibitor: Imidazoles
(Antifungal)
Squalene epoxidase
●
It is involved in fungal ergosterol biosynthesis.
squaline epoxidase
●
ergosterol
squaline
- Inhibition of the enzyme lead to accumulation of
squaline within the cell
toxic to the organism
Dihydrofolate reductase
- Responsible for conversion of dihydrofolate to
tetrahydrofolate
folic acid synthesis
- Folic acid is required in the synthesis of
thymidylate (pyrimidine) and of purine
nucleotides and thus for DNA synthesis
Dihydrofolate reductase Inhibitores:
- Methrotrexate (anticancer),
- pyrimethamine (antiprotozoal, antimalarial),
- Trimethoprim (antibacterial)
Thymidylate synthase
●
Responsible for synthesis of thymidylate
Inhibitor of Thymidylate synthase
- 5-Fluorouracil & 5-fluorodeoxyuridine (cancer)
HIV Reverse
Transcriptase
Retrovirus
Reverse transcriptase
(Viral RNA dependent DNA polymerase)
DNA copy of the viral RNA
HIV Reverse Transcriptase Inhibitors
MOA:
-Competitive inhibition of HIV-1 reverse transcriptase
- Incorporated into the growing viral DNA chain → cause
termination
- Most have activity against HIV-2 as well as HIV-1.
- Eg. 3’-azido-2’,3’-dideoxythymidine (AZT)
IV. Enzymes as drug targets
Enzyme
- Mono amine oxidase
Drug/ Inhibitores/Significant
Ephedrine, Amphetamine
(MAO)
(Increases the level of catecholamine)
- Acetyl cholinesterase
Neostigmine (Used in glaucoma).
- HMG CoA reductase
Lovastatin, Compactin (Inhibit
cholestrol biosynthesis)
- ACE
Enalapril, Captopril (Control the BP)
IV. Enzymes as drug targets
Enzyme
- Cyclooxygenase
(COX)
Drug/ Inhibitores/Significant
Paracetamol (Nonselective NSAIDS), Aspirine
(Antiplateletes)
Cilicoxibe (Selective COX-II
Inhibitores)
lanosterol
14-α-demethylase
Imidazoles (Antifungal)
(a fungal cytochrome-haem
P450 enzyme)
squalene epoxidase
Terbinafine (Antifungal)
IV. Enzymes as drug targets
Enzyme targeting
Drug
Dihydrofolate reductase
Antifolates: methrotrexate (cancer),
(Folate metabolism)
pyrimethamine (protozoa, malaria)
trimethoprim (bacteria)
Thymidylate synthase
5-Fluorouracil &
(Pyrimidine metabolism)
5-fluorodeoxyuridine (cancer)
HIV-Reverse transcriptase
3’-azido-2’,3’-dideoxythymidine (AZT)
HIV proteases
Ritonavir, saquinavir (clinical trial phase)
SUMMARY
 Enzymes
are biological catalysts present in every cell of the body.
 Isoenzyme
patterns can give information about organ-specific
disease.
 Important
enzymes in the investigation of heart disease are CK,
LDH and AST.
 Important
enzymes in the investigation of liver disease are AST,
- Creatine kinase has three isoenzymes: CK-MM, CK-MB and
CK-BB.
- LDH has five isoenzymes.
- Increased levels of acid phosphatase are found in prostate cancer.
Thank you