Altering enzyme activity

• What can affect activity of enzyme in vivo?

  Inhibitors, physical factors, cellular regulation
• How does temperature affect enzymes?

  Increases collisons between substrate and active site occur more frequently as moleciles move faster. Thermal agitation disrtupt the weak bonds that stabilise the protein conformation, leading to thermal denaturartion
• How does pH affect enzymes?

  pH influences protein conformation and electrostatic interactions between enzyme and substrate (ionisation).

  Optimum between pH 6–8 for most enzymes
• What is committed step?

  first dedicated reaction , often the rate limiting step
• what is the final product of the pathway often?

  An inhibitor of the enzyme that catalyses the committed step (to stop unnecessary production)
• What is the structure of 3-phosphoglycerate dehydrogenase?

  Tetramer of 4 identical subunits
• What occurs when serine binds to 3-phosphoglycerate dehydrogenase?

  Lowers Vmax
• what is allosteric effect?


  an effect at one site on a molecule caused by binding of a molecule at a second, distinct site
• what are positive regulators?

  cooperative binding
• what is negative regulators?

  allosteric inhibitos
• Do allosteric enzyme obey michaelis-menten?

  No
• What does positive cooperativity to plot?

  makes its sigmoidal
• What is the T-state?

  tense = low activity
• what is the R-state?

  Relaxed = high activity
• what does a change of T to R mean?

  decreases in Km and increases reaction rate
• Example of an allosteric regulation:

  Aspartate carbamoyltransferase (ACTase)
• What is the use of ACTase?

  First committed step in pyrimidine synthesis
• What is the structure of ACTase?

  multi-subunit enzyme
• what are the two subunits of ACTase?

  6 catalytic and 6 regulatory subunits
• What is the transition state of ATCase?

  PALA (stable)
• what does binding of PALA to ACTase do?

  A conformational change from the T-state to R-state
• what does binding of CTP to ACTase do?

  Binds to regulatory subunits and stabilised the T-state
• How is ACTase regulated?

  enzyme activity is regulated by the balance between substrate and end-point product
• what is a isoenzymes?

  Different versions of the same enzyme with different catalytic properties
• Are isoenzymes encoded by different genes?

  yes but from the same gene families
• What does lactate dehydrogenase do?

  Converts lactate to pyruvate and backwards
• what are the two forms of LDH?

  H
• what is the H form?

  higher affinity for substrates,

  allosterically inhibited by pyruvate

  optimised to convert lactate to pyruvate to provide fuel for aerobic metabolism