Enzymes and Their Function

• Enzymes catalyze reactions

Definition of Terms

• Apoenzyme: the protein part of an enzyme, needs a cofactor to work.
• Holoenzyme: the complete, active enzyme.
• Active site: place where the enzyme's reaction occurs.
• Allosteric site: a site different from the active site.
• Isoenzymes: different forms of an enzyme, catalyze the same reaction.

Enzyme categories:

• Oxidoreductase: performs oxidation/reduction reactions, examples include LDH, G6PD, and Malate dehydrogenase
• Transferase: moves groups from one substrate to another, such as AST, ALT, CK, and GGT
• Hydrolase: causes hydrolysis, examples include ACP, ALP, 5'NT, AMS, LPS, and CHS
• Lyase: removes groups without hydrolysis, such as Aldolase
• Isomerase: interconverts isomers
• Ligase: joins two substrate molecules, includes synthases

Hepatic Enzyme Profile

• ALP (Alkaline Phosphatase): liver, kidney, bone, placenta, intestine, and WBC sources uses B-glyceroPO4 and p-nitrophenylPO4 substrates, Bodansky, Shenowara Jones, King-Armstrong, or Bessy Lowry-Brock methods resulting in a pH of 10 that is greatly elevated in Paget's disease, avoid using EDTA-Citrate-Oxalate
• ALT (SGPT): Liver and RBC sources using Alanine a-keto substrate and Reitman-Frankel (DNPH) methods resulting in a liver-specific marker with marked elevation with viral hepatitis, De ritis ratio: >1 = viral; <1 = non-viral
• LD (Lactate Dehydrogenase: all tissues sources using Wacker's method (forward) or Wrobleuski La Due (reverse) or Wrobleuski Cabaud Berger Broida methods resuting in a NAD+ (cofactor), LD4 and LD5 enzyme that can be stored at 25°C for up to 24 hours
• GGT (Gamma-Glutamyl Transferase): Canaliculi of hepatic cells, Kidney, Prostate, and Pancreas sources using Gammaglutamyl p-nitroanilide substrate and SZAZ methods resulting in a marker that is most sensitive for alcoholic hepatitis
• ChE (Cholinesterase): Pseudo- Liver sources using Acetylcholine and Pseudo- Michael; Ellman methods, ChE: CNS, RBC, Lungs, Spleen, Pseudo: Liver, Succinylcholine (relaxant)

Cardiac Enzyme Profile

• CK (Creatine Kinase): Cardiac, skeletal, and brain tissues sources using Tanzer-Gilvarg (forward) or Oliver-Rosalki (reverse) methods for identifying anesthetic poisoning, CK-BB (fastest migrating; most anodal), CK-MB, CK-MM (slowest; least anodal)
• AST (SGOT): comes from the Liver, heart, skeletal muscle, the source uses Aspartate a-keto substrate and Karmen Method (Ph 7.5; 340 nm) methods that is sensitive indicator of AMI & Duchenne disorder
• LD is from All tissues sources using Wacker method (forward) - pH 8.8 or Wrobleuski La Due (reverse) - pH 7.2 or Wrobleuski Cabaud Berger Broida methods using LD1 (anodic & heat stable) used to check the LD2 (heat stable & major isoenzyme in the sera of healthy persons) of the LD5 when checking for LD5 (cathodic & cold labile), Flipped ratio: LD1>LD2
• Myoglobin: Responsible for O2 supply of striated muscle
• Troponin: 3 subunits I (inhibitory), T (tropomyosin-binding) & C (calcium-binding)

Acute Pancreatitis Profile

• AMS: Salivary glands, Pancreas sources using Saccharogenic or lodometric/Amyloclastic Chromogenic or Kinetic methods to check Pancreatic AMS: diastase, Salivary AMS: ptyalin or check for MicroAMS: unbound (free), MacroAMS: bound to IgG and IgA, test identifies for Earliest pancreatic marker with its Smallest enzyme in size to check Salivary AMS: inhibited by wheat germ lectin
• LPS: Pancreas sources uses Olive Oil/Triolein (pure form of TAG) in Cherry-Crandall or Sigma-Tietz Titration methods to end up with the End product of Fatty Acids identified by its Most specific pancreatic marker

Prostatic Cancer Profile

• ACP (Acid Phosphatase): RBC and Prostate sources using Chemical Inhibition Test and Organophosphates through RBC-ACP: inactivated by Cu++, unaffected by Tartrate or through P-ACP: unaffected by Cu++, inactivated by Tartrate methods being Very labile (add 5M acetate buffer/citrate tablet to preserve)
• PSA (Prostate Specific Antigen): sample using Tartrate methods, is Most useful for tumor marker for prostate cancer with a Reference Range: of 0-4ng/mL

Acute Myocardial Infarction Markers:

• Myoglobin: onset at 1-3 hours, peaks at 5-12 hours, lasts 18-30 hours
• Troponin I: onset at 3-4 hours, peaks at 10-24 hours, lasts 7 days up to 10-14 days
• Troponin T: onset at 3-6 hours, peaks at 12-18 hours, lasts 5-10 days
• CK-MB: onset at 4-6 hours, peaks at 12-24 hours, lasts 48-72 hours
• AST: onset at 6-8 hours, peaks at 24 hours, lasts 5 days
• LDH: onset at 12-24 hours, peaks at 48-72 hours, lasts 10-14 days