Effects of Inhibitors on Enzyme-Controlled Reactions

• Zymogens/Proenzymes

  Enzymes secreted as inactive proteins and activated by cleaving
• Holoenzyme

  An active enzyme, containing all necessary coenzymes and cofactors
• Apoenzyme

  An inactive enzyme, lacking its coenzyme or cofactor
• Precursor activation

  When a precursor enzyme undergoes a change in shape (particularly in tertiary structure), often caused by a cofactor or the action of another enzyme, to be activated
• Prosthetic groups


  Small cofactors that are tightly and permanently pound to form a permanent feature of the enzyme (e.g. an Fe ion as a prosthetic group to haemoglobin)
• Coenzymes

  An organic molecule serving as a cofactor. Most vitamins, such as Vitamin B3, have coenzyme derivatives, such as NADP, in metabolic reactions.
• Cofactors

  Any non-protein molecule or ion that is required for the proper functioning of an enzyme. Cofactors can be permanently bound to the active site or may bind loosely with the substrate during catalysis
• End-product Inhibition

  When reactants from a reaction act as inhibitors to the enzyme producing them, creating a negative-feedback system that prevents reactant overproduction
• Irreversible inhibition

  The change to the enzyme is permanent or long-term, preventing it from functioning. They are often toxic (e.g. cyanide), but not always (e.g. PPIs used to treat indigestion)
• Reversible inhibition

  The change to the enzyme is non-permanent
• Non-competitive inhibition

  Inhibition by a molecule that binds to an enzyme at a location outside the active site (Allosteric site) and inhibits the enzyme's function. (Vmax cannot be achieved regardless of substrate concentration)
• Competitive inhibition

  Inhibition of an enzyme's ability to catalyze a chemical reaction via a non-reactant molecule that competes with the substrate(s) for access to the active site. (If there is enough substrate, Vmax can still be achieved)
• Enzyme inhibitors


  A chemical that interferes with an enzyme's activity
• Optimum pH

  the pH at which an enzyme achieves maximum activity
• pH

  Hydrogen ion concentration/Whether a substance is acidic, neutral or basic
• Optimum temperature

  The temperature at which an enzyme is most active and at which the temperature coefficient (Q10) stops increasing
• Denaturation from temperature

  Increased temperature causes the bonds holding the proteins together to vibrate more until the bonds strain and break, resulting in a change in the tertiary structure. This changes the shape of the enzyme, including its active site, and it is considered to be denatured.
• temperature coefficient (Q10)


  A measure of how much the rate of a reaction increases with a 10 °C temperature increase. (In enzyme-controlled reactions, this number is normally taken as two, meaning the rate of reaction doubles every 10 degrees)
• Protease

  An enzyme that breaks down proteins and peptides
• Trypsin

  Trypsin is a protease. Proteins are broken down into peptides and then broken down into amino acids by other proteases. Trypsin is produced in the pancreas and released into the small intestine in pancreatic juice. Amino acids produced are absorbed by the cells lining the digestive system and absorbed into the bloodstream
• Digestion of starch

  - Starch is broken down into maltose (a disaccharide) by amylase, which is produced by the salivary glands into the mouth and the pancreas into the small intenstine

  - Maltose is then broken down into glucose, which is a monosaccharide, by maltase in the small intestine
• Extracellular enzymes

  Enzymes that act outside of the cell in which they are produced (e.g. enzymes breaking down nutrients)
• Intracellular enzymes

  enzymes that catalyse reactions within the cell and control cell metabolism (e.g. catalase breaking down hydrogen peroxide)
• Vmax

  maximum initial velocity or rate of an enzyme-catalysed reaction.
• Induced fit hypothesis

  - The shape of the enzyme's active shape changes shape slightly as the substrate enters.

  - The initial interaction between enzyme and substrate is weak, but these interactions rapidly induce changes in the enzyme's tertiary structure that strengthen binding, putting strain on the substrate molecule. This weakens particular bonds in the substrate and thereby lowers the activation energy.
• Lock and Key Hypothesis

  - An area within the tertiary structure of the enzyme has a shape that is complementary to the shape of a specific substrate molecule. This area is called the active site.

  - In the same way that only the right key will fit a lock, only a specific substrate will fit the active site of an enzyme. This is called the Lock and Key Hypothesis.

  - When the substrate is bound to the active site, an enzyme-substrate complex is formed and the substrate(s) then react and the product(s) are formed in an enzyme-product complex which are then released, leaving the enzyme unchanged and able to take part in subsequent reactions

  - The substrate is held in such a way by the enzyme that the right atom-groups are close enough to react. The R-groups within the enzyme's active site will also interact with the substrate to form temporary bonds, putting strain on the bonds within the substrate and helping the reaction.
• Mechanism of enzyme action

  - Molecules in a solution move and collide randomly

  - For a reaction to happen, molecules need to collide in the right orientation

  - When high temperatures and pressures are applied, the kinetic energy and speed of molecules increase and therefore so do the number of successful collisions and the overall rate of reaction

  - Enzymes are specific to one biochemical reaction

  - A level of energy is needed for most reactions to start (activation energy) and sometimes the energy needed is too high to occur under normal conditions. Enzymes help molecules collide successfully and therefore reduce the activation energy needed.
• Catabolic

  A process in which large molecules are broken down
• Anabolic

  A process in which large molecules are built from small molecules
• Enzyme

  - A biological catalyst

  - Globular proteins that interact with substrate molecules to cause them to react at a mush faster rate without needing harsh environmental conditions
• ATP


  An example of a coenzyme that binds temporarily to enzyme active sites, providing energy for cellular processes.
• Vitamin B3

  An example of a coenzyme that binds temporarily to enzyme active sites, participating in various metabolic reactions.
• Coenzymes


  Organic non-protein molecules that temporarily bind to an enzyme's active site, assisting in the catalytic reaction.
• Chloride ions


  A cofactor for the enzyme amylase, necessary for its proper function in breaking down starch into smaller sugar molecules.
• Cofactors


  Inorganic ions or small organic molecules required for the proper functioning of certain enzymes.
• Carbonic anhydrase


  An enzyme that contains a zinc-based prosthetic group, facilitating the rapid conversion of carbon dioxide to bicarbonate ions.
• Prosthetic groups

  Non-protein organic molecules that permanently bind to a functioning protein molecule, aiding in its stability or catalytic activity.
• Non-enzyme helper molecules


  Vitamins and minerals that assist enzymes in their function by providing necessary cofactors or coenzymes.
• Penicillin


  An inhibitor of a bacterial enzyme involved in cell wall formation, halting bacterial reproduction and leading to cell death.
• Antibiotics


  Substances that kill or inhibit the growth of microorganisms, often by targeting specific enzymes essential for their survival.