BIOC 212 Lecture Notes - Lecture 42: Glycerol, Aldehyde, Electronegativity
29 May 2018
School
Department
Course
Professor
Metabolism IV
Ubiquitination Enzymes
• Other use of thioester bond = ubiquitination
• E1: ATP --> AMP + PPi adds Ub
o E1-Ub thioester is high energy bond
o Attach the Ub onto the E1 enzyme
o Use double hydrolysis of ATP to AMP and pyrophosphate, to attach Ub onto
cysteine side chain as high energy thioester
o Same energetics as Coenzyme A
• E1-Ub to E2-Ub
o Thioester bond energies are similar
o Transfer Ub from E1 to E2
o Can go back & forth between E1 & E2 since same energetics
• E2-Ub + E3 --> Substrate-Ub
o Isopeptide bond (lysine-Ub) is lower energy so favorable
o Thioester bond is higher in energy than isopeptide bond onto lysine
• So transfer of Ub from E2 to substrate is energetically favored
PDI Regeneration
• FADH2 high energy, oxidized by O2
o Oxidized by molecular oxygen to make peroxide
o Constantly generating FAD, which is there to oxidize Ero1
• FAD always present to oxidize Ero1
o FAD-Ero1 ready drives PDI
• Therefore, PDI always oxidized and ready for substrate; driven by chain of
energetics
o PDI gets reduced when catalyzes S-S bond formation in substrate
o Regenerated by Ero1, which is regenerated/oxidized by FAD
• New substrates are translocated into ER, so pathway never reaches equilibrium
o Keep putting new polypeptides without disulfides, and keep exporting
products from ER (proteins with complete disulfide bonds)
o Have two ways to drive the reaction forward
How is Organization Maintained
• Constant energy input required to maintain organization in the cell
• In humans:
