Enzyme 3

• how do isoenzyme arise?

  Homologous genes that have diverged during evolution
• what are isoenzyme?


  slightly different forms of an enzyme in the same organism but which catalyse the same reaction
• what does enzyme kinetics tells?

  • catalytic activity of enzyme in solution
  • purity
  • efficiency in relation to different substrate/ active site structure
  • characterising the efficiencies of isoenzyme
  • effectiveness of inhibitors nad mode of action
• What did ludwig Wilhelmy discover?

  initial rate is proportional to substrate concentration (using sucrose and acid)
• What did Adrian brown discover?

  Low substrate conc (at constant enzyme conc) the rate is proportional to substrate conc.

  High substrate conc rate becomes independent - rate is being limited by substrate enzyme complexes form
• what did Adrain Brown use?

  Hydrolysis of sucrose by yeast, invertase (enzyme)
• who made the rectangular hyerbola curve?

  Leonor Michaelis and Maud Menten
• what are Vmax units?

  maxium velocity

  units = units of y axis (rate units)
• what is Vmax?


  The maximum possible rate of the reaction at that particular enzyme concentration
• why is Vmax an estimate?

  have to extrapolate due to infinite [S] required
• what is Km?


  The substrate conc at which the velocity of reaction is half Vmax
• what is km as well?


  The substrate concentration that half of the active site are occupied
• what is Km independent on?

  amount of enzyme and substrate present
• What does Km define?


  The interaction between enzyme and substrate molecules, CONSTANT
• What is Vmax independent on?

  amount of substrate
• what is Vmax dependent on?

  Amount of enzyme
• what are some michaelis-menten assumptions?


  The reaction is a single substrate reaction

  K2 in the simplified equation assumes that there is no reverse component to this step of the mechanism
• what are the steps of the mechanism in K2?

  Reverse catalysis

  Product inhibition
• what does using the initial velocity help with?

  lower product inhibition and reverse catalysis
• what does high substrate is not proportionate?


  Substrate concentration cancel out so V=Vmax
• why does low Km mean high affinity?

  low substrate concentration is needed to occupy half of enzyme active sites
• what does drug design use?


  drugs/ inhibitor needs lower Km than substrate so it binds more effectively to enzyme active site
• How many alcohol dehydrogenase classes are there?

  6
• what do different isoenzymes do?

  alter properties such as isoelectric point or surface charge
• what can't you do with Vmax?

  compare efficiencies between to totally unrelated enzyme with unrelated substrates
• What is turnover number?


  Vmax/[Et]
• what is [Et]?


  [E] + [ES]
• what are the two types of reciprocal plot?

  Lineweaver-Burk plot

  Eadie-Hoftsee plot
• which plot uses double reciprocal plot?

  lineweaver-burk