Clinical (Diagnostic & Therapeutic ) importance
of Enzymes and isoenzymes
Objectives
• List the clinically important enzymes and
isoenzymes.
• State which of the enzymes and isoenzymes are
found in which tissues
• Outline different ways of measuring plasma enzyme
• Describe plasma enzyme changes in different
diseases.
Circulatory system enzymes
serum enzymes




Functional serum enzyme
responsible for reaction taking place in blood
e.g; clotting of blood
Non functional serum enzymes
do not have their function in blood but they are
present because of wear and tear of the tissue IN
CONSTANT level
INTRODUCTION
• Injury or death of tissues can cause the release of
tissue-specific enzymes into the bloodstream.
• Elevated enzyme levels are often indicators of
tissue problems, and are used in the diagnosis of
diseases.
• Enzyme activities in the body fluids are altered by
pathological processes so, its measurement is used
for disease investigation.
Measurement of serum enzymes
 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
 Organ specificity- but not absolute specificity in
spite of same gene content.

Most enzymes are present in most cells-differing amounts
 Time course of disease
Enzymes routinely measured
NAME OF THE ENZYME
PRESENT IN
Aspartate Amino
Heart and Liver
transferase (AST)
Serum glutamateoxaloacetate transaminase
(SGOT)
Alanine Amino transferase
(ALT)
Serum glutamate-pyruvate
transaminase (SGPT)
Heart and Liver
Enzymes routinely measured
NAME OF THE ENZYME
PRESENT IN
Alkaline Phosphatase (ALP)
Bone, intestine and
other tissues
Acid Phosphatase (ACP)
Prostate
 glutamyl Transferase (
GT)
Liver
Creatine kinase (CK)
Muscle Including
cardiac muscle
Lactate Dehydrogenase
(LDH)
Heart, liver, muscle,
RBC
 Amylase
Pancreas
Myocardial Infarction
Enzyme Assays that are Carried out in
Mayocardial Infarction
 Commonly done:
•
•
•
Creatine kinase (CK)
Aspartate Amino transferase (AST)
Lactate Dehydrogenase (LDH)
Myocardial Infarction ( MI )
• Necrosis of the myocardium, but not angina
pectoris release of CK, AST and LDH
into the circulation.
• CK is the first to rise (activity within 6 h of
MI ).
• Total CK reaches a peak at 24-36 h.
• In uncomplicated cases, CK returns to
normal within 3 days.
Myocardial Infarction ( MI )
• Serum AST  more slowly ( maximum
activity within 48 h) and returns to normal
in 4-5 days.
• No significant elevation in LDH seen for the
1st 24 h (reaches maximum at about 3 days
& remain  for up to 8 days).
• The enzyme is relatively non specific to
myocardial tissue.
Liver Diseases
Hepatic Necrosis
Hepatitis
Cholestasis
Jaundice
Hepatocellular Damage
Liver Enzymes ( ALT, AST, GGT, ALP, LDH)
Measurement of serum enzyme activities for :
a - Differential Diagnosis of Jaundice.
b - Monitoring of drug toxicity.
• ALT is more specific than AST.
• Hepatocellular disease has only modest effect on
ALP & GGT (up to 3 times the upper limit of
normal)
• In Cholestasis, Higher values of ALP & GGT
due to  synthesis
Alanine aminotransferase (ALT)
•Widely distributed, although the largest
amounts found in the liver.
•Smaller amounts occur in the heart but
usually remains normal after MI .
•Congestive cardiac failure release from the liver
•More specific for liver disease than AST.
Aspartate aminotransferase (AST)
•
This enzyme is widely distributed in the body.
• Main sources: Heart, liver, skeletal muscle, and kidney.
• Useful in the diagnosis of MI, liver disorders and muscle
damage.
•Causes of serum AST levels:.
Liver diseases: Hepatitis, hepatic necrosis , cholestasis
•Cardiac disease: Myocardial Infarction.
•Diseases of skeletal muscle: Crush injury,trauma,myopathy
•From Erythrocytes:
Hemolysis
Alkaline phosphatase (ALP)
• Widely distributed, high concentrations in
intestines, liver, bone, spleen, placenta and kidney.
• The main sources of serum ALP are the
hepatobiliary tree and bone disorders.
• Elevated levels during healing of fractures , active
growth and during the 3rd trimester of pregnancy.
•  serum ALP activity in liver disease is mainly
due to Cholestasis.
• Decreased levels are found in the inherited
condition
Alkaline phosphatase (ALP)
Causes of increased serum alkaline phosphatase enzyme activity:
Physiological :
- Infancy
- Puberty
- Pregnancy
- Intestinal isoenzymes
- Hyperparathyroidism
- Osteomalacia, rickets
- Paget’s disease of bone
- Osteomyelitis
Bone disease:
Hepatobiliary disease:
Others:
- Hepatitis
- Cholestasis
- Cirrhosis
Carcinoma of the bronchus
Acid phosphatase (ACP)
Found in prostate, bone, liver, spleen, kidney, RBCs
and platelets
Primarily used to diagnose prostate cancer .
 In other prostatic conditions e.g. prostatitis, benign
prostatic hypertrophy.
In other non prostatic conditions e.g. hemolysis, Paget’s
disease, metastatic carcinoma of the breast & Gaucher’s
disease.
Prostate- Specific Antigen(PSA): an enzyme occurs in
prostatic tissue and  in cases of metastatic carcinoma
Amylase (AMS)
HYDROLASES THAT SPLIT COMPLEX POLYSACCHARIDES.
- CA+2 REQUIRING METALLOENZYME
NORMAL LEVEL: 50-120 U/L INCREASES DRASTICALLY IN
ACUTE PANCREATITIS ALSO IN MUMPS
SOURCES :
1. PANCREAS (P-TYPE)
2. SALIVARY GLANDS (S-TYPE)
3. INTESTINAL MALIGNANCY
CLINICAL SIGNIFICANCE : DIAGNOSIS AND MONITORING OF
PANCREATITIS
Lipase (LPS)
• Breaks down fat into monoacylglycerol and free
fatty acids.
• Primarily from the pancreas.
• Used to diagnose acute pancreatitis.
• Pancreatic lipases :
Almost exclusively used clinically in the
investigation of pancreatitis.
- Increase within 2 - 12 hours of acute attack.
- May remain elevated for many days .
- More specific to acute pancreatitis than
amylase.
Specificity of Enzymes :
• Greater specificity is achieved in three ways:
1. Interpreting investigations in the light of
clinical features
2. Isoenzyme determination:
-  AST may be due to MI or Hepatitis so, it
makes
confusion in diagnosis to be confirmed by
LDH levels.
-  ALP in Cholestasis & bone diseases :
- Differentiated by  bilirubin &
transaminase levels in Cholestasis .
- Confirmed by  GGT in Cholestasis.
NAME OF THE ENZYME
Conditions in which level of
activity in serum is elevated
Aspartate Amino
Myocardial infarction, Liver
transferase (AST)
disease especially with liver cell
damage
Serum glutamateoxaloacetate transaminase
(SGOT)
Alanine Amino transferase
(ALT)
Serum glutamate-pyruvate
transaminase (SGPT)
Liver disease especially with liver
cell damage
Alkaline Phosphatase
(ALP)
Liver disease- biliary obstruction
Osteoblastic bone disease-rickets
Acid Phosphatase
(ACP)
Prostatic carcinoma
 glutamyl Transferase
( GT)
Liver disorder like liver
cirrhosis
Creatine kinase (CK)
Myocardial infarction and
skeletal muscle
disease(muscular dystrophy
Lactate
Myocardial infarction, other
Dehydrogenase (LDH) diseases like liver
disease.some blood
diseases
 Amylase
Acute pancreatitis
ISOENZYMES
• Catalyze the same reaction
• Two or more polypeptide chains
• Different polypeptide chains are products of
different genes
• Differ in AA sequence and physical properties
• May be separable on the basis of charge
• Are tissue specific
Diagram illustrating the origin of Isoenzymes
LACTATE DEHYDROGENASE (LDH)
converts pyruvate to lactate (and vice versa)
LDH occurs as a tetramer of 2 different subunits H &
M:
(product of 2 diff. gene)
normal LDH2 is high in serum but after MI LDH1
rises
increase of total is seen in
hemolytic anemia,hepatocellular
damage,carcinomas,leukemias & any condition of
five isoenzymes of LDH that occurs as a dimer of 2
different subunits H &M
,
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 kinase is associated with ATP regeneration in
muscle and nervous tissue.
• Elevated blood levels of CK are used as indicators of MI,
muscular dystrophy, and stroke.
• CK occurs as a dimer of 2 different subunits, M and B.
- CK-BB: Brain .
- CK-MB: cardiac muscle.
- CK-MM: Muscle type.
• CK-MB is released from cardiac muscle cells after MI.
Isoenzyme
Composition Present in
name
Elevated in
CK-1
CNS diseases
CK-2
CK-3
BB
Brain
MB
Acute
Myocardium
myocardial
/ Heart
infarction
MM
Skeletal
muscle,
Myocardium
„ Cardiac enzymes“
The figure is adopted from the book: Devlin, T. M. (editor): Textbook of Biochemistry with Clinical Correlations, 4th
ed. Wiley-Liss, Inc., New York, 1997. ISBN 0-471-15451-2
ENZYMES IN THERAPY
• Substitution of missing production of digestive
enzymes – digestive enzymes – pepsin trypsin…
• Removal of deposits of death tissue or fibrin (e.g. in
lungs, eyes), treatment of skin defects – proteinases,
nucleases, collagenase
• Acceleration of fibrinolysis in lungs embolization
(activation of plasmin and plasminogen) –
• streptokinase, urokinase
Thank you
Quiz
1.An activated enzyme consisting of polypeptide
chain and a cofactor is called:
• A.Apoenzyme
B.Holoenzyme
2.Which one forms the raw material for
coenzymes?
• A.Viitamins
B.Carbohydrates
3.A cofactor made of inorganic ion which is
detachable is called
• A.Prosthetic group B.Coenzyme
4. Enzymes _________ the activation energy of a
chemical reaction
• A.Increases
B.Decreases
5. Three dimensional dcavity bearing a specific
charge by which the enzyme reacts with its
substrate is called
• A.Active site
B.Binding site
6. Which step causes activation of catalytic site of
an enzyme?
• A.Change in pH of the surroundings.
• B.Formation of Enzyme Susstrate complex
7. If the concentration of enzyme is kept
constant and amount of substrate is increased
a point is reached where increase in
substrates concentration does not affect the
reaction rate because of
• A.Enzymes get denatured at higher substrate
conc.
• All the active sites on enzyme molecule are
occupied.
7. f more substrate to already occurring
enzymatic reaction is added and there is no
effect on the rate of the reaction what is the
form given to this situation:
• A.Saturation B.Denaturation
8.Optimal temperature of enzymes present in
human body is
• A.27C
B.37C
9. A chemical substance which can react (in place
of substrate) with the enzyme but is not
transformed into product/s and thus blocks the
active site temporarily or permanently is called
• A.Co-enzyme B.Blocker
C.Inhibitor
10 The structure of an enzyme is altered by:
• A.Irreversible inhibitor B.Reversible inhibitor