The intermembrane space is the region between the inner membrane and theouter membrane of a mitochondrion or a chloroplast. The main function of the intermembrane space is oxidative phosphorylation.
Channel proteins called porins in the outer membrane allow free movement of ionsand small molecules into the intermembrane space. This means that it is essentially continuous with the cytosol in terms of the solutes relevant for the functioning of these organelles. Enzymes destined for the mitochondrial matrix or the stroma can pass through the intermembrane space via transport throughtranslocators. These are known as translocase of the outer mitochondria membrane (TOM) and translocase of the inner mitochondrial membrane (TIM) in mitochondriaand translocase of the outer chloroplast membrane (TOC) and translocase of the inner chloroplast membrane (TIC) in chloroplasts. It tends to have a low pH because of the proton gradient which results when protons are pumped from themitochondrial matrix into the intermembrane space during electron transport. The structures responsible for this are coenzyme Q, NADH coenzyme Q oxidoreductasecomplex (complex I), succinate-coenzyme Q oxidoreductase complex (complex II), and coenzyme Q-cytochrome c oxidoreductase complex (complex III).
[edit]Intermembrane space of mitochondria
Because of channels in the outer membrane of the mitochondria, the content of the intermembrane space is similar to that of the content of the cytoplasm.
[edit]Intermembrane space of chloroplast
The intermembrane space of the chloroplast is extremely small, somewhere from 10-20 nm thick.
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