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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 enzymesserum 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
• 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.
INTRODUCTION
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 damageOrgan 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 transferase (AST)Serum glutamate-oxaloacetate transaminase (SGOT)
Heart and Liver
Alanine Amino transferase (ALT)Serum glutamate-pyruvate transaminase (SGPT)
Heart and Liver
Enzymes routinely measuredNAME 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.
• 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.
Myocardial Infarction ( MI )
Liver Diseases Hepatic Necrosis
Hepatitis Cholestasis
Jaundice Hepatocellular Damage
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
Liver Enzymes ( ALT, AST, GGT, ALP, LDH)
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.
• 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
Aspartate aminotransferase (AST)
•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)
Alkaline phosphatase (ALP) Causes of increased serum alkaline phosphatase enzyme activity:
Physiological :
Bone disease:
Hepatobiliary disease:
Others:
-Infancy -Puberty
-Pregnancy -Intestinal isoenzymes
-Hyperparathyroidism -Osteomalacia, rickets
-Paget’s disease of bone -Osteomyelitis
-Hepatitis -Cholestasis
-Cirrhosis
Carcinoma of the bronchus
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
Acid phosphatase (ACP)
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
Amylase (AMS)
•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.
Lipase (LPS)
• 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.
Specificity of Enzymes:
NAME OF THE ENZYME Conditions in which level of activity in serum is elevated
Aspartate Amino transferase (AST)Serum glutamate-oxaloacetate transaminase (SGOT)
Myocardial infarction, Liver disease especially with liver cell damage
Alanine Amino transferase (ALT)Serum glutamate-pyruvate transaminase (SGPT)
Liver disease especially with liver cell damage
Alkaline Phosphatase (ALP)
Liver disease- biliary obstructionOsteoblastic 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 Dehydrogenase (LDH)
Myocardial infarction, other 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 risesincrease of total is seen in hemolytic anemia,hepatocellular damage,carcinomas,leukemias & any condition of necrosis.
, five isoenzymes of LDH that occurs as a dimer of 2 different subunits H &M
Isoenzyme name
Composition Composition Present in Elevated in
LDH1 ( H4) 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 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.
Creatine kinase (CK)
Isoenzyme name Composition Present in Elevated in
CK-1 BB Brain CNS diseases
CK-2 MB Myocardium/ Heart
Acute myocardial infarction
CK-3 MMSkeletal muscle, Myocardium
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‑ ‑ ‑ ‑
„ Cardiac enzymes“
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.Carbohydrates3.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.Decreases5. 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