Creatine kinase (CK) and lactate dehydrogenase (LDH) are important isoenzymes that can help diagnose conditions like acute myocardial infarction. CK has three isoenzymes - CK-BB in the brain, CK-MB in cardiac muscle (80% of total), and CK-MM in skeletal muscle (94-100% of normal serum). Increased CK-MB more than 6% of total CK indicates AMI. LDH has five isoenzymes - LD1 highest in heart and LD5 in skeletal muscle. Elevated LD1 and flipped LD1>LD2 pattern indicates AMI. Aspartate aminotransferase (AST) also rises with AMI and

1. IsoEnzymes
Dr Rina Das Mehta
Professor
MM College of Pharmacy, MM(DU)

2. Isoenzymes
• Isoenzymes – are enzymes that differ in amino acid
sequence but catalyze the same chemical reaction.
• They have similar catalytic activity, but are different
biochemically or immunologically.
• Different forms may be differentiated from each
other based on certain physical properties
• electrophoretic mobility,
• differences in absorption properties
• or by their reaction with a specific antibody

3. Creatine Kinase (CK)
• Action –This enzyme is associated with the regeneration
and storage of high energy phosphate (ATP).
• It catalyzes the following reversible reaction in the body.

4. Creatine Kinase (CK)
• High concentrations of CK in:
• skeletal muscle,
• cardiac muscle
• and brain tissue
• Increased plasma CK activity is associated with
damage to these tissues
•  CK is especially useful to diagnose:
• Acute Myocardial Infarction (AMI)
• Skeletal muscle diseases ( Muscular Dystrophy )

5. Creatine Kinase (CK)
• CK has 3 isoenzymes
• Each isoenzyme is composed of two different
polypeptide chains (M & B)
•CK - BB (CK1) Brain type
•CK - MB (CK2) Cardiac type or hybrid type
•CK – MM (CK3) Muscle type
• Normal serum consists of approximately 94% to 100%
CK-MM
• Cardiac muscle CK is 80% CK-MM and 20% CK-MB

6. Creatine Kinase (CK)
• BB migrates fastest to anode than MB & MM
• The major isoenzyme in the sera of healthy people is the
MM form.
• Values for the MB isoenzyme range from undetectable to
trace (<6% of total CK).
• It also appears that CK-BB is present in small quantities in
the sera of healthy people

7. Diagnostic Significance
• The value of CK isoenzyme separation can be found principally in
detection of myocardial damage.
• Cardiac tissue contains significant quantities of CK-MB,
approximately 20% of all CK-MB.
• increased CK – MB ( > 6% of the total CK activity ) is a strong
indication of AMI
• Post AMI CK-MB
• CK-MB increases 4 – 8 hours postAMI
• Peaks at 12 - 24 hours postAMI
• Returns to normal 48 - 72 hours

8. Lactate Dehydrogenase (LDH)
• Catalyzes interconversion of lactic and pyruvic acids
• It is a hydrogen-transfer enzyme
• NAD is used as coenzyme
• High activities in heart, liver, muscle, kidney, and RBC
• Lesser amounts: Lung, smooth muscle and brain

9. LDH Isoenzymes
• Because increased total LDH is relatively
non-specific, LDH isoenzymes can be
useful
• 5 isoenzymes composed of a cardiac (H)
and muscle ( M ) component
• LD - 1 ( HHHH ) Cardiac , RBCs
• LD - 2 ( HHHM ) Cardiac , RBCs
• LD - 3 ( HHMM ) Lung, spleen, pancreas
• LD - 4 ( HMMM ) Hepatic
• LD - 5 ( MMMM ) Skeletal muscle
• LD-1 is the fastest towards the anode

10. Diagnostic Significance
• LDH is elevated in a variety of disorders.
• in cardiac,
• hepatic,
• skeletal muscle,
• and renal diseases,
• as well as in several hematologic and neoplastic disorders
• The highest levels of LD-1 are seen in pernicious
anemia and hemolytic disorders
• LD-3 with pulmonary involvement
• LD-5 predominates with liver & muscle damage

11. Diagnostic Significance
• In healthy individuals
• LD-2 is in highest quantity then LD-1, LD-3, LD-4
and LD-5
• Heart problems: 2-10 x (Upper Limit of Normal)
ULN in acute MI
• If problem is not MI, both LD1 and LD2 rise, with
LD2 being greater than LD1
• If problem is MI, LD1 is greater than LD2.
• This is known as a flipped pattern

12. Aspartate Aminotransferase
(AST, SGOT, GOT)
•The transamination reaction is important in
intermediary metabolism because of its function
in the synthesis and degradation of amino acids.
•The ketoacids formed by the reaction are
ultimately oxidized by the tricarboxylic acid cycle
to provide a source of energy.

13. Diagnostic Significance
• The clinical use of AST is limited mainly to the
evaluation of hepatocellular disorders and
skeletal muscle involvement.
• Post AMI
• Rises 6 – 8 hours
• Peaks at 24 hours
• Returns to normal by day 5
• AST levels are highest in acute hepatocellular
disorders, viral hepatitis, cirrhosis.
• Viral hepatitis may reach 100 x ULN