PS1

• (3a) Biotin is covalently attached to a lysine of PC. The type of bond or functional group that joins them is an amide. The role of biotin is a CO2 carrier.
• (3b) Where/why does PC activity require ATP hydrolysis? Why does it req. an energy input?

  ATP hydrolysis is required to phosphorylate bicarbonate, which activates it so that CO2 can be given to biotin. The bicarbonate that is available is inaccessible, or too stable, until ATP hydrolysis is used to activate it.
• (3c) Acetyl-CoA is an allosteric activator of PC, where PC remains inactive until acetyl-CoA is bound. Why is it a good idea to regulate PC activity w/ acetyl-CoA?

  Acetyl-CoA feeds into the TCA cycle. But the TCA cycle requires oxaloacetate. PC can be used to produce oxaloacetate that is needed.
• How does PC deficiency cause lactic acid buildup? (Where does lactic acid come from?)

  Lactic acid builds up as fermentation occurs, which is an anaerobic alternative route after glycolysis to regenerate NAD+. The lactate produced can be run through gluconeogenesis, which requires PC in the step of carboxylating pyruvate to oxaloacetate. With PC deficicency, gluconeogenesis cannot properly occur, and it is gluconeogenesis that is used to eliminate lactate and prevent buildup.
• (4b) If patients with genetic mutation of PC were found to have PC enzymes that could still bind biotin, would it make sense for their mutation to be near the N-terminus or C-terminus of PC?

  N-terminus. The domain where biotin binds, the BCCP domain, is at the C-terminus of biotin. A mutation there would result in PC enzymes that cannot bind biotin.
• (4c) A population w/ PC mutation at one terminus has PC that can bind biotin but is still inactive, why?

  The population's mutation is at the N-terminus, which contains the BC domain. The BC domain is essential for PC functioning because it activates bicarbonate and catalyzes the addition of CO2 to biotin. Additionally, it must bind multiple substrates or cofactors like bicarbonate, ATP, biotin, and Mg2+.