Isoenzymes

Isoenzymes

• Multiple forms of an enzyme which differ in physical and chemical properties and catalyze the same reaction as an enzyme.
• Isoenzymes are produced by a single gene and some may result from more than one gene.
• Isoenzymes can be separated by:
1-Heat inactivation
2-Chemical inhibition
3-Electrophoretic techniques (specific)

ISOENZYMES

Catalyze the same reaction.

Differ in AA sequence and physical

properties.

Separable on the basis of charge.

Are tissue specific.


• Different Isoenzymes may arise from different tissues and their specific detection may give clues to the site of
• pathology.

Electrophoresis

Is a technique by which separation of Movement of charged particles through an electrolyte when subjected to electrical field.

Advantages of Isoenzyme measurement

• Isoenzyme variants are derived from different tissue sources.
• So separation renders increased specificity to enzyme analysis.
• Tissue or organ effected can be detected ( where isoenzyme elevation occurs)

Types

• CPK (creatinine Phospho Kinase)
• Troponin
• LDH (Lactate Dehydrogenase)
• ALP (Alkaline phosphatase)
• Aldolase
• Amylase


CPK-Creatinine Phospho kinase
CPK Isoenzymes are performed when the total CPK level is elevated.
Isoenzyme testing can help differentiate the source of the damaged tissue.
CPK is an enzyme found predominantly in the heart, brain, and skeletal muscle.
CPK is composed of 3 Isoenzymes that differ slightly in structure:
CPK is a dimer made up of 2 subunits called B for brain and M for muscle.

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

CREATINE KINASE (CK)

CPK- Isoenzymes

CPK-1 (also called CPK-BB) is concentrated in the brain and lungs
CPK-2 (also called CPK-MB) is found mostly in the heart
CPK-3 (also called CPK-MM) is found mostly in skeletal muscle
Because the CPK-1 isoenzyme is predominately found in the brain and lungs, injury to either of these organs (for example, stroke or lung injury due to a pulmonary embolism) are associated with elevated levels of this isoenzyme.


• Isoenzyme name
• Composition
• Present in
• Elevated in
• CK-1
• BB
• Brain
• CNS diseases
• CK-2
• MB
• Myocardium Heart
• Acute myocardial infarction
• CK-3
• MM
• Skeletal muscle, Myocardium

CPK (CK)

Creatinine Phospho kinase or Creatinine Kinase catalyses the conversion of creatinine to creatinine Phosphate.
Creatinine +ATP Creatinine kinase creatinine phosphate +ADP Creatinine Phospho kinase
Normal level: 15-100U/L (males)
: 10-80 U/L (females)


Sample: in serum it is estimated and not increased in hemolysis.

Atherosclerosis

Is a condition in which arteries are blocked to a greater or lesser extent by deposition of cholesterol plaques , leading most commonly to coronary heart disease by blocking of coronary arteries i.e
( myocardial infarction MI).

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

LDH-Isoenzymes

The LDH has five Isoenzymes which are:
LDH-1 (H4) is found mainly in the heart.
LDH-2 ( H3M1) Reticuloendothelial system.
LDH-3 (H2M2) is found in the lungs.
LDH-4 ( H1M3) in the kidney, placenta, and pancreas, and
LDH-5 ( M4) in liver and striated (skeletal) muscle.
Normally, levels of LDH-2 are higher than those of the other Isoenzymes

• 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


DescriptionLDH
LDH is found in the cells of almost all body tissues.
Because this enzyme is actually composed of five different Isoenzymes, however, analysis of the different LDH isoenzyme levels in the blood can help in the diagnosis of some diseases.

LDH
LDH is an oxidoreductase enzyme whose activity is necessary for the reversible reaction in which Pyruvate and lactate are inter converted. It is important in glycolysis.
LDH Isoenzyme is a tetramer with 4 subunits. The subunit may be either H (heart) or M (muscle) .

LDH and Heart Attack

One of the most important diagnostic uses for the LDH Isoenzymes test is in the differential diagnosis of myocardial infarction or heart attack.
The total LDH level rises within 24-48 hours after a heart attack, peaks in two to three days, and returns to normal in approximately five to ten days.
The LDH-1 isoenzyme level, however, is more sensitive and specific than the total LDH.


LDH and Heart Attack
Normally, the level of LDH-2 is higher than the level of LDH-1.
An LDH-1 level higher than that of LDH-2, a phenomenon known as "flipped LDH," is strongly indicative of a myocardial infarction.
The flipped LDH usually appears within 12-24 hours after a heart attack.
A normal LDH-1/LDH-2 ratio is considered reliable evidence that a heart attack has not occurred.

LACTATE DEHYDROGENASE IN MI

Alkaline Phosphatase (ALP)

• Isoenzymes are five:
• ALP-1 present in liver increased in obstructive jaundice, biliary cirrhosis.
• ALP-2 in bone increased in rickets and Pagets
• ALP-3 in placenta increase in 2nd and 3rd trimester of pregnancy and decrease indicates placental insufficiency and foetal death.

Alkaline Phosphatase (ALP)

• 4. ALP-4 in intestine increased in intestinal disease and after gastrectomy surgery
• 5. ALP-5 in kidney increases in kidney disorders.
In normal serum liver and bone fractions are present.
Abnormal ALP Isoenzymes Regan and nagao are present in carcinomas and metastasis.
Normal level: 40-125 U/L


Amylase
• Salivary in normal serum 60% increased in Parotitis/ mumps
• Pancreatic 40% increased in pancreatitis
The peak levels are seen between 5-12hours after onset of disease and returns to normal level with in 2-4 days.
Normal level: 50-120 IU/L

Aldolase

• Aldolase-A present in muscle increased in muscular dystrophies.
• Aldolase-B in liver increased in hepatitis.
• Aldolase-C in brain
Normal level: 1.5-7 U/L

Acid phosphatase

Present in Prostate, RBC and platelets.
Increased in Prostate cancer, Gaucher’s disease and thromboembolic disorders
Normal level: 2.5-12 U/L

Enzymes in Liver diseases

The following enzymes when elevated are useful in the diagnosis of liver diseases and disfunction due to viral hepatitis, toxic hepatitis, cirrhosis and hepatic necrosis
1.Alanin transaminas(ALT).
2. Aspartate transaminase (AST).
3.Lactate dehydrogenase (LDH).


The enzymes that markedly increase in intrahepatic and extra hepatic cholestasis are
4-Alkaline Phsphatase.
5- Nucleotidase.

Coenzymes: the protein part of the enzyme on its own is not always adequate to bring about the catalytic activity and many enzymes require certain non protein small additional factor regarded as cofactor these cofactors are called (Coenzymes)
Coenzymes are non protein organic low molecular wt associated with enzyme function.It differs from enzyme by physical, chemical and immunological properties.

Coenzymes for B complex vitamins:

Most of the coenzymes are the derivatives of water soluble vit B, the biochemical function of B-complex are exerted through their respective coenzymes.
Non Vit Coenzymes:
Organic substances which has no relation with vit but function as coenzymes Ex: ATP,CDP(cytidine monophosphate) UDP(uridine diphosphate)
NAD,NADP FMN ,FAD.

Enzymes as therapeutic agents;

Enzymes are used as drug for treatment of medical problem
Streptokinase; is a useful for clearing the blood clot .
Streptokinase activates plasma plasminogen to plasmin which in turn attacks fibrin to convert into soluble products