When speaking of Mitchell's chemiosmotic hypothesis, it's common to consider the proton gradient as measured from the mitochondrial intermembrane space to the mitochondrial matrix. But textbooks say the outer mitochondrial membrane is freely permeable to molecules smaller than ~5kDa. Does this mean that the pH of the mitochondrial intermembrane space is equal to the cytosolic pH?
Lewis J et al., 2002 have been reported that "small molecules equilibrate freely across the outer membraneof the mitochondrion, the pH in the intermembrane space is the same as in the cytosol".
Kindly, have a look at the link below.
https://www.ncbi.nlm.nih.gov/books/NBK26894/
Fawaz, thank you for your answer. Here is a follow-up question. Does this mean that mitochondria can only control the the pH of the matrix and the pH in the cytosol/intermembrane space is actually determined largely by plasma membrane proton transporters and cytosolic buffers?
Dear Prof. Robert Phair
According to Puff N, et al., 2018 have reported that the pH approximately 8 in the matrix whereas in the cytosol/intermembrane space ESTIMATED to be near to 7.4.
From this study, I can say YES. Mitochondria only control the pH of the matrix while the pH in the cytosol/intermembrane determined by cytosolic buffers and other factors as you mentioned above.
Article pH Sensing by Lipids in Membranes: The Fundamentals of pH-dr...
https://www.ncbi.nlm.nih.gov/books/NBK21528/
Regards
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