ENZYMES &CLINICAL ENZYMOLOGY
Prepared by: Assistant professor Dr.Sumreena Mansoor
Vignette 5
•
Presenting complaint: A 50 year old man complains of severe retrosternal pain
radiating to his left arm and jaw.
•
Medical History: Severe chest pain on exertion that is relieved by sitting down. He
is hypertensive and is on ACE inhibitors for the last two years
•
Examination: Anguished, dyspneic male, with hand clutched to chest. He is
nauseated and has vomited a few times.
•
Family History: His father died of a Myocardial Infarction and his younger brother
is also taking ACE inhibitors.
•
Investigations: EKG, CK-MB, LDH, Troponin I & T
•
Emergency treatment: Injection streptokinase
•
Diagnosis: Myocardial Infarction (MI)
ENZYME DIAGNOSTICS
ISOENZYMES
Catalyze the same reaction.
Differ in AA sequence and physical
properties
Separable on the basis of charge.
Are tissue specific.
Isoenzymes
Different Isoenzymes may arise from
different tissues and their specific
detection may give clues to the site of
pathology.
ENZYMES
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
Creatine kinase (CK)
Muscle Including cardiac muscle
Lactate Dehydrogenase (LDH)
Heart, liver, muscle, RBC
 Amylase
Pancreas
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
LACTATE DEHYDROGENASE IN MI
CREATINE KINASE (CK)
 Creatine kinase is a dimer made of 2 monomers
occurs in the tissues
 Skeletal muscle contains M subunit, Brain contains
B subunits
 Three different isoenzymes are formed
Isoenzyme
name
Composition
Present in
Elevated in
CK-1
BB
Brain
CNS diseases
CK-2
MB
Myocardium/
Heart
Acute myocardial
infarction
MM
Skeletal
muscle,
Myocardium
CK-3
ALANINE TRANSAMINASE (ALT) AND
ASPARTATE TRANSAMINASE( AST)
- Oxoglutarate + L-aspartate
Aspartate
aminotransferase (AST)
L- glutamate + oxaloacetate

- Oxoglutarate + L-alanine
Alanine
aminotransferase
(ALT)
L - glutamate + pyruvate
Alanine transaminase (ALT) and Aspartate transaminase (AST)
enzymes are the most abundantly present in the liver and is
elevated in blood as a result of leakage from damaged cells

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
LEVELS OF ENZYMES IN DISEASES
INVOLVING LIVER DAMAGE
In viral hepatitis
Rapid
rise
in
transaminases
(AST & ALT) in
serum occurs even
before
bilirubin
rise is seen
LEVELS OF ENZYMES IN MYOCARDIAL
INFARCTION
AST and CK rise in
6 hours following
acute
myocardial
infarction
LDH are elevated
much
later
and
remains high for a
longer period of
days
LDH
CK
CK-MB
AST
SUMMARY

Enzymes are biological catalysts present in every cell of the body.

An enzyme will act on a specific substrate yielding a product.

An isoenzyme is a genetic variant produced largely within a
specific tissue.

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,
ALT.

Creatine kinase has three isoenzymes: CK-MM, CK-MB and CK-BB.

LDH has five isoenzymes.

Alkaline phosphatase can be used in the investigation of liver and
bone disease.

Increased levels of acid phosphatase are found in prostate cancer.