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INTERMEMBRANOUS SPACE

Intermembranous (or, intermembrane) space is the compartment confined between the outer membrane of a mitochondrion and the inner one. There are substrates, enzymes and some metabolites in it. The distance between the membranes is 10 to 20 nm. The outer membrane contains many repeated molecules of transport protein forming wide hydrophilic channels in the lipid bilayer. It resembles a sieve admitting all molecules of mass up to 10000 dalton, including small proteins. That is why the chemical composition of the intermembranous space is equivalent to the composition of the cytosol at least concerning molecules of small size.