BIOC 212 Lecture Notes - Lecture 60: Hydrolysis, Atp Hydrolysis, Atp Synthase
29 May 2018
School
Department
Course
Professor
Metabolism XXII
Electrochemical Gradient
• Proton pumping generates an electrochemical gradient
• The result of proton pumping is a gradient of more protons in the IMS than the
matrix
o Chemiosmotic gradient
o Across the inner membrane of the mitochondria --specialized membrane
that is very impermeable to protons outside the complexes
• Can maintain a pH gradient that is then used to generate ATP
• Voltage gradient is around 180-190mV
• pH gradient is about 0.5 units
• Like the pH gradient, the voltage potential allows biological regulation by having
molecules that like slightly more positive/negative environments
o Inner membrane voltage gradient is calibrated effectively to make these
molecules stable in the electron orientation they want
o Helps orient proteins as they transit into the mitochondria from the cytosol
• Positive matrix targeting signal is pulled into the IMS
• Due to voltage gradient generated by proton pumping
• pH difference between matrix & ISM is about 0.5 units
o As long as pKa difference between oxidized and reduced from > 1 unit, can
have range where are exceeding the basicity of the matrix and the acidity of
the IMS as transit electron through the chain
Both Gradients are Used by Mitochondria
• There are various transporters that move metabolites across the IM
o Very impermeable membrane --requires protein translocators to move any
molecule across, including H+
o If want to move a large molecule like ADP or ATP across, need to have
large binding site for it and energy to pump it
• Voltage gradient is required for ATP-ADP exchange
o Voltage gradient drives the exchange since ATP has an extra negative
charge, and thus prefers to leave towards the positive side of the IM
o ADP will be more favorable to move towards the negative side since are
effectively moving a charge across the membrane
• pH gradient is required for pyruvate and phosphate transporters (and for other
metabolites)
o Used to drive a lot of other metabolite transporters
o Pyruvate & phosphate importers have a binding site for a proton as well as
for their substrate
