Enzymes & Kinetics

Enzymes are proteins that catalyse biochemical reactions — speeding them up without being consumed. A single enzyme molecule can process thousands of substrate molecules per second. Enzymes work by lowering the activation energy of a reaction — the energy needed to get the reaction started. They do this by holding the substrate in exactly the right position and shape. Importantly, enzymes do not change whether a reaction is possible — they just make it happen much faster.

Many medicines work by blocking enzymes. There are two main types: Competitive inhibition — the drug looks similar to the substrate and competes for the active site. Like two people trying to sit in the same chair. Adding more substrate can push the inhibitor out. Example: statins (lower cholesterol by blocking HMG-CoA reductase). Non-competitive inhibition — the drug binds a different site on the enzyme, changing its shape so it no longer works properly. More substrate cannot overcome this. Example: heavy metal poisoning.

When tissue is damaged, enzymes leak from cells into the blood. Measuring these gives doctors clues about what organ is injured: Troponin I/T — released from damaged heart muscle. The best test for a heart attack (myocardial infarction). ALT / AST — liver enzymes. High levels suggest liver damage or hepatitis. Amylase / Lipase — pancreatic enzymes. High levels suggest pancreatitis (inflamed pancreas).