L.Noha Soliman

Biochemistry(BMS)

Enzymes

Objectives

Enzyme Regulation: 1. Feedback control.

2. Proenzymes.

3. Isoenzymes.

Enzymes as diagnostic tools.

1. Feedback control:Regulation process where the product of a series of enzyme-catalyzed reactions inhibits an earlier reaction in the sequence.

Enzyme Regulation

2. Proenzymes (Zymogens): They are inactive precursors of enzymes.

Most digestive and blood-clotting enzymes exist in the zymogen form, until activated.

Must have polypeptide chain portion removed otherwise not active.

Enzyme Regulation

2. Proenzymes (Zymogens): Ex. Trypsin ( Digestive enzyme):

Synthesized and stored as trypsinogen. No enzyme activity. Active only after a six- amino acid fragment is removed. Removal of amino acid fragment changes primary and

tertiary structure Active form.

Enzyme Regulation

3.Isozymes or Isoenzymes:

Enzyme Regulation

Different form of the same enzyme.

They perform the same catalytic function.(Catalyze same reactions but are formed from structurally different polypeptides).

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

ENZYMES AS

DIAGNOSTIC TOOLS

How?

The measurement of the serum levels of numerous enzymes has been shown to be of diagnostic significance.

This is because the presence of these enzymes in the serum indicates that tissue or cellular damage has occurred resulting in the release of intracellular components into the blood &this increases the level of certain enzymes in blood according to the damaged organ.

Information from enzymes measurements

in serum? Presence of disease.

Organs involved.

Etiology /nature of disease: differential diagnosis.

Extent of disease-more damaged cells-more leaked enzymes in blood.

Measurement of enzyme activity

Enzyme activity is expressed in International unit (IU):

-It corresponds to the amount of enzymes that catalyzes the conversion of one micromole (mol) of substrate to product per minute.

WHAT ARE THE ENZYMES MOST

USED IN

THE DIAGNOSIS OF

CERTAIN DISEASES?

Plasma enzymes

Non functional

**For example:-

3-Alanine transaminase(ALT) 4-Aspartate transaminase(AST)

5-Alkaline phosphatase 6-Acid phosphatase

7-Amylase & Lipase enzymes

Isoenzymes1-Lactate dehydrogenase(LDH)2-Creatine kinase(CK)

Functional

Lactate dehydrogenase(LDH)

Lactic acid Pyruvic acid

NAD NADH+H

LDH is elevated in myocardial infarction, blood disorders.

It is a tetramer 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.

Lactate dehydrogenaseisoenzymes

Isoenzyme name

Composition Composition Present in Elevated in

LDH1 ( H4) HHHH Heart, RBC

myocardial infarction

LDH2 (H3M1) HHHM Heart, RBC

myocardial infarction

LDH3 (H2M2) HHMM lungs and spleen

leukemia

LDH4 (H1M3) HMMM lungs and spleen

viral hepatitis

LDH5 (M4) MMMM Skeletal muscle, Liver

Skeletal muscle and liver diseases

Creatine kinase (CK)

Creatine Creatine phosphate

ATP ADP

Creatine kinase is a dimer made of 2 monomers.

Skeletal muscle contains M subunit, Brain contains B subunits.

Three different isoenzymes are formed.

(Phosphocreatine – serves as energy reserve during muscle contraction)

Creatine kinase (CK) isoenzymes

Isoenzyme name Composition Present in Elevated in

CK-1 BB BrainCNS diseasesbrain tumors

CK-2 MB HeartAcute myocardial infarction

CK-3 MM Skeletal muscle

Skeletal muscle diseases

Alanine transaminase(ALT)

It is also called Serum glutamic pyruvic transaminase(SGPT).

This enzyme is found predominantly in hepatocytes. It increases in liver & heart diseases. ALT is more specific for liver disease than AST.

Aspartate transaminase(AST)

It is also called Serum glutamic oxaloacetic transaminase(SGOT) It increases in liver & heart diseases.

Alkaline phosphatase**It is found in the bone , liver, intestine, placenta.

**Increases mainly in bone and liver diseases.

Acid phosphatase**is found in the prostate, red blood cells, bone, liver, and pancreas.

** Mostly used to detect prostatic carcinoma.

Amylase and lipase enzymes increase in diseases of the pancreas as acute pancreatitis.

Summary-Enzymes as diagnostic markers

Major diagnostic use Origin EnzymeMyocardial infarction Heart, liver,

muscle, RBCLactate dehydrogenase (LDH)

Muscle diseaseMyocardial infarction

Skeletal MuscleHeart MuscleBrain

Creatine kinase (CK)

Viral hepatitis Heart and Liver Alanine aminotransferase (ALT) Serum glutamate-pyruvate transaminase (SGPT)

Liver and heart disease Heart and Liver Aspartate aminotransferase (AST) Serum glutamate-oxaloacetate transaminase (SGOT)

Liver and bone disease Hepatobiliary tree Bone, placenta

Alkaline phosphatase (ALP)

Prostate cancer Prostate, erythrocytes

Acid phosphatase (ACP)

Acute pancreatitis Pancreas, Salivary glands

Amylase

Acute pancreatitis Pancreas Lipase

THANKS

Many