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.

IsoenzymesDifferent 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 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

LACTATE DEHYDROGENASE IN MI

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)CREATINE KINASE (CK)

Isoenzyme name

Composition Present in Elevated in

CK-1 BB Brain CNS diseases

CK-2 MBMyocardium/ Heart

Acute myocardial infarction

CK-3 MMSkeletal muscle, Myocardium

Alanine aminotransferase

(ALT)

Aspartate aminotransferase (AST)

ALANINE TRANSAMINASE (ALT) AND ASPARTATE TRANSAMINASE( AST)

- Oxoglutarate + L-aspartate

L- glutamate + oxaloacetate L - glutamate + pyruvate

- Oxoglutarate + L-alanine

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 hepatitisRapid rise in transaminases (AST & ALT) in serum occurs even before bilirubin rise is seen

LEVELS OF ENZYMES IN MYOCARDIAL INFARCTION

CKCK-MB

AST

LDH

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

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.