Enzymes Biochemistry (BMS) L.Noha Soliman

Objectives Enzyme Regulation: Enzymes as diagnostic tools. 1. Feedback control. 2. Proenzymes. 3. Isoenzymes. Enzymes as diagnostic tools.

Enzyme Regulation 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: 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?

**For example:- Plasma enzymes Functional Non functional Isoenzymes 1-Lactate dehydrogenase(LDH) 2-Creatine kinase(CK) Isoenzymes 3-Alanine transaminase(ALT) 4-Aspartate transaminase(AST) 5-Alkaline phosphatase 6-Acid phosphatase 7-Amylase & Lipase enzymes

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 dehydrogenase isoenzymes Isoenzyme name Composition Present in Elevated in LDH1 ( H4) HHHH Heart, RBC myocardial infarction LDH2 (H3M1) HHHM LDH3 (H2M2) HHMM lungs and spleen leukemia LDH4 (H1M3) HMMM viral hepatitis LDH5 (M4) MMMM Skeletal muscle, Liver Skeletal muscle and liver diseases

Creatine kinase (CK) Creatine Creatine phosphate ATP ADP (Phosphocreatine – serves as energy reserve during muscle contraction) Creatine kinase is a dimer made of 2 monomers. Skeletal muscle contains M subunit, Brain contains B subunits. Three different isoenzymes are formed.

Creatine kinase (CK) isoenzymes Isoenzyme name Composition Present in Elevated in CK-1 BB Brain CNS diseases brain tumors CK-2 MB Heart Acute 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.

**It is found in the bone , liver, intestine, placenta. 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 Enzyme Myocardial infarction Heart, liver, muscle, RBC Lactate dehydrogenase (LDH) Muscle disease Skeletal Muscle Heart Muscle Brain Creatine kinase (CK) Viral hepatitis Heart and Liver Alanine aminotransferase (ALT) Serum glutamate-pyruvate transaminase (SGPT) Liver and heart disease 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 Pancreas Lipase

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