from the mitochondrial matrix to the IMS by these respiratory complexes. As a result, an electrochemical gradient is generated, which is combined by forces due to a H+ gradient (pH gradient) and a voltage gradient (membrane potential). The pH in the IMS is about 0.7 unit lower than the one in the matrix and the membrane potential of the IMS side becomes more positively charged than the matrix side. This electrochemical gradient from the IMS to the matrix is used to drive the synthesis of ATP in the mitochondria. Apoptosis Releasing of cytochrome c from the IMS to the cytosol activates procaspases and triggers a caspase cascade leading to apoptosis. Intermembrane space of chloroplasts The intermembrane space (IMS) of the chloroplast is exceedingly small, from 10 to 20 nm thick. Unlike the IMS of the mitochondria, the IMS of the chloroplast does not seem to have any obvious function. The translocase of the outer membrane (TOC) and the translocase of the inner membrane (TIC) mainly assist the translocation of chloroplast precursor proteins Chaperone involvement in the IMS has been proposed but still remains uncertain. The eukaryotic Hsp70, which is the heat shock protein of 70 kDa, typically localized in the cytoplasm is also found in the IMS of chloroplasts. The resulting hypothesis states that co-localization of Hsp70 is important for efficient translocation of protein precursors into and across the IMS of chloroplasts. Intermembrane space of nuclear envelopes The nuclear envelope is composed of two lipid bilayer membranes that are penetrated by nuclear pores and separated by a small intermembrane space, which is often called the perinuclear space. The perinuclear space is usually about 20-40 nm wide. The perinuclear translocation of certain proteins and enzymes were studied and results showed that perinuclear space was important for genome integrity and gene regulation. References Cell anatomy