Prelim LEC Lesson 4 Miscellaneous Enzymes.pdf

CREATINE KINASE (CK) E.C. 2.7.3.2 MW: 82,000 Da Associated with ATP regeneration in contractile or transport system (constant concentration of ATP in the muscle needed for any sudden burst of exercise) CREATINE KINASE (CK) Isoenzymes ISOENZYMES TISSUE SOURCE ELECTROP...

CREATINE KINASE (CK) E.C. 2.7.3.2 MW: 82,000 Da Associated with ATP regeneration in contractile or transport system (constant concentration of ATP in the muscle needed for any sudden burst of exercise) CREATINE KINASE (CK) Isoenzymes ISOENZYMES TISSUE SOURCE ELECTROPHORESIS CK-MM Skeletal muscles CK-3 CK-MB Heart muscle CK-2 CK-BB Brain tissues CK-1 CREATINE KINASE (CK) Isoenzymes CK-Mi – MW: 350, 000 – bound to the exterior surface of the inner mitochondrial membranes of muscle, brain, and liver (will only be present in serum in cases of extensive tissue damage) CREATINE KINASE (CK) Isoenzymes Macro-CK – largely comprises CK-BB complexed with Ig (IgG) – CK-MM + lipoproteins  CK-MB Myocardial Infarction Rise: within 4-8 hours after the onset Peak: 12-24 hours Return to normal: within 48-72 hours Note: CK-MB is sensitive but not specific to MI.  LACTATE DEHYDROGENASE (LD) E.C. 1.1.1.27 L-Lactate: NAD+ Oxidoreductase Catalyzes the interconversion of lactate to pyruvate Pyruvate to lactate in anaerobic glycolysis Coenzyme: NAD+  LACTATE DEHYDROGENASE (LD) Tissue Sources Widely distributed in the body – Heart – Liver – Skeletal muscle – Kidney – Erythrocytes – Lung – Smooth muscle – Brain  LACTATE DEHYDROGENASE (LD) Myocardial Infarction Rise: within 12-24 hours after the onset Peak: 48-72 hours Remain elevated: 10 days – LD 1 > LD 2 LD flipped pattern Suggestive of AMI  GAMMA-GLUTAMYL TRANSFERASE (GGT) E.C. 2.3.2.2 (5-Glutamyl) Peptide: Amino Acid-5- Glutamyl-Transferase Involved in the transfer of the gamma- glutamyl residue from gamma-glutamyl peptides to amino acids, H2O, and other small peptides  GAMMA-GLUTAMYL TRANSFERASE (GGT) PHYSIOLOGY Has not been clearly established Involved in peptide and protein synthesis Regulation of tissue glutathione levels Transport of amino acids across cell membranes  GAMMA-GLUTAMYL TRANSFERASE (GGT) TISSUE SOURCES – Kidney – Brain – Prostate – Pancreas – Liver (canaliculi of the hepatic cells)  GAMMA-GLUTAMYL TRANSFERASE (GGT) DIAGNOSTIC SIGNIFICANCE Elevated in all hepatobiliary disorders – Biliary tract obstruction Increased in patients receiving enzyme-inducing drugs – warfarin, phenobarbital, phenytoin Increased in chronic alcoholism/excessive alcohol consumption Useful in monitoring abstention from alcohol Normalizes 2-3 weeks after cessation of drinking  GAMMA-GLUTAMYL TRANSFERASE (GGT) DIAGNOSTIC SIGNIFICANCE Biliary Bone disease Obstruction GGT Normal Increased ALP Increased Increased  GAMMA-GLUTAMYL TRANSFERASE (GGT) SZASZ ASSAY  GLUCOSE-6-PHOSPHATE DEHYDROGENASE (G6PD) E.C. 1.1.1.49 D-Glucose-6-Phosphate: NADP+ 1- Oxidoreductase Catalyzes the oxidation of glucose-6-phosphate to 6- phosphogluconate or 6-phosphogluconolactone Reaction is important in the pentose-phosphate shunt of glucose metabolism with the ultimate production of NADPH  GLUCOSE-6-PHOSPHATE DEHYDROGENASE (G6PD) DIAGNOSTIC SIGNIFICANCE RBC – Maintain NADPH in reduced form – Required to regenerate glutathione from the oxidized to the reduced state Reduced glutathione protects Hgb from oxidation Low G6PD = low NADPH = low reduced glutathione= hemolysis  GLUCOSE-6-PHOSPHATE DEHYDROGENASE (G6PD) ASSAY A red cell hemolysate is used to assay for deficiency of the enzyme; serum is used for evaluation of enzyme elevations ANGIOTENSIN-CONVERTING ENZYME (ACE) E.C. 3.4.15.1 Angiotensin I-Converting Enzyme Other names: Kininase II and Peptidyl-Dipeptidase A Hydrolysis of peptide bonds at a free C-terminus releasing a dipeptide in the reaction Cleaves His-Leu sequence in Angiotensin 1 to form Angiotensin 2 Contains Zinc in its active site ANGIOTENSIN-CONVERTING ENZYME (ACE) Tissue-bound, with much lower levels circulating in plasma Predominantly found in endothelial cell membranes throughout the body Lungs and Testes – rich in ACE ANGIOTENSIN-CONVERTING ENZYME (ACE) Measurement Measured by its ability to cleave synthetic peptides, releasing hippuric acid ANGIOTENSIN-CONVERTING ENZYME (ACE) Causes of Abnormal Results SARCOIDOSIS – Abnormal collection of inflammatory cells called granulomas may appear on the body (overreaction of the immune system) – Any part of the body can be affected but the most commonly affected areas are the lungs, skin, eyes and lymph nodes  5'-nucleotidase (5'n) E.C. 3.1.3.5 5’-Ribonucleotide Phosphohydrolase Is a cytoplasmic membrane-bound phosphatase Acts only on nucleotides Functions in extracellular adenosine production, nutrient absorption, and cell proliferation  5'-nucleotidase (5'n) A metalloenzyme (zinc) Widely distributed in the body, predominantly attached to cell membranes (like ALP and GGT) Plasma levels are predominantly derived from the liver Commonly used to determine if the source of an elevated ALP is from liver or bone  5'-nucleotidase (5'n) Measurement Difficult because other phosphatases like ALP can cleave the substrate – Remedy: to use ALP inhibitors like theophylline and levamisole Chelating agents inhibit activity (EDTA inhibits enzyme activity)  CHOLINESTERASE (ChE) E.C. 3.1.1.7 Acetylcholinesterase or ‘true’ cholinesterase (choline esterase 1) or RBC cholinesterase E.C. 3.1.1.8 Pseudocholinesterase (choline esterase 2) or plasma cholinesterase  CHOLINESTERASE (ChE) “True” AChE: found in the nervous system, neuromuscular junctions, and RBCs  CHOLINESTERASE (ChE) E.C. 3.1.1.8 Pseudocholinesterase or butyrylcholinesterase is produced by the liver and hydrolyzes choline esters  CHOLINESTERASE (ChE) Measurement Ellman’s Method – Substrate: acylthiocholine ester – Released thiocholine react with Ellman's reageant – Product: 5-mercapto-2-nitro benzoic acid  CHOLINESTERASE (ChE) Measurement – PseudoChE: Serum – True ChE: Hemolysate of washed RBC  CHOLINESTERASE (ChE) Why measure? PseudoChE – Organophosphate Insecticides Irreversible inhibitors of both AChE and PChE PChE activity falls before AChE activity – PChE reflects acute toxicity; AChE reflects chronic exposure  CHOLINESTERASE (ChE) Why measure? AChE – Useful in organophosphate exposure and poisoning – Qualitative analysis in amniotic fluid may be useful in the diagnosis of neural tube defects (normally absent in AF)  CHOLINESTERASE (ChE) Neural tube defects  Aldolase (ald) EC 4.1.2.13 D-fructose-1,6-bisdiphosphate D-glyceraldehyde-3- phosphate-lyase  Aldolase (ald) Isoenzymes: – Aldolase A Skeletal muscles – Aldolase B WBC, liver, kidneys – Aldolase C Brain tissue