Environment's Impact on Enzymes

• Regulatory molecules


  Bind to enzymes and are either excitatory or inhibitory so turns their activity up or down
• Cofactors


  Non-protein helper molecules that enzymes can only be active when bound to. Common ones are Fe and Mg ions. DNA polymerase needs Mg2+ to function
• Compartmentalization


  Storing enzymes in specific areas to prevent them from doing damage or keeping them in the right conditions to be active
• Feedback inhibition


  When key metabolic enzymes are inhibited by the product of the end pathway they control, keeping more end product from being produced to make sure optimal amounts are being produced. Usually at the first committed step of the pathway
• Activators


  Molecules that increase enzyme activity
• Inhibitors


  Molecules that decrease enzyme activity
• Reversible inhibitors


  Enzyme inhibitors who can bind to multiple enzymes
• Competitive inhibition


  When an inhibitor binds to an enzyme and stops it from binding to a substrate in doing so. Can be "outdone" when there is enough substrate, so functionally useless if overpowered
• Noncompetitive inhibition


  When the inhibitor does not bind to the active site, but instead binds somewhere else that effectively stops it from doing its job. Works no matter how much substrate because it poisons the enzyme so it cant work at all
• Allosteric regulation


  Any form of regulation where a regulatory molecule (activator or inhibitor) binds to an enzyme someplace other than the active site
• Allosteric site


  Non-active site that regulatory molecules bind to
• Allosteric enzymes


  Typically have multiple active sites located on multiple protein subunits. When allosteric regulators bind to the enzyme, all sites work less or more well
• Cooperativity


  When the substrate itself becomes an allosteric activator
• Coenzyme


  Subset of cofactors that are organic (carbon-based) like vitamins
• First committed step


  First part of the metabolic pathway that is effectively irreversible
• ATP is an allosteric inhibitor of the enzymes for cellular respiration. This means that when there is a high concentration of ATP, the enzymes are inhibited. Its byproduct, ADP, is an activator, so when a lot of the ATP was used up, cellular respiration goes back up
• Initial velocity (V0)


  Amount of product being created as soon as an enzyme is added to a substrate
• Enzyme kinetics graphs track initial velocity of an enzyme over different amounts of substrate (with the same amount of enzyme). Then a curve is drawn to fit the points. Generally V0 goes up as substrate increases until it plateaus at some point (enzyme saturation)
• Maximum velocity (Vmax)


  Y value (initial rate of reaction) in an enzyme kinetics graph where the graph plateaus
• Km


  Substrate concentration that gives you the halfway point to Vmax. Unlike Vmax, which depends on concentration, this will stay constant for any given enzyme of the same kind. Lower = higher affinity for the substrate, higher = lower affinity for the substrate
• Competitive inhibitors eventually get out-competed and its enzyme will reach Vmax, just taking longer, so Km looks higher. Noncompetitive inhibitors will have a normal looking graph, just less than its actual potential, because the enzymes it binds to are effectively not there. The apparent Km stays the same though because of the existing enzymes working normally
• Michaelis - Menten enzymes


  Enzymes whose efficacy can generally be expressed on a curve with a plateau around Vmax with Km at the halfway point
• Allosteric enzymes


  Have different efficacy curves because the binding to substrate at one active site generally increases their odds to bind to more substrate at their other active sites
• Cooperative enzymes


  Enzymes with high sensitivity to changes in substrate concentrations that have a "switch" that lets their velocity change very quickly, and so have an S-shaped curve