Intermembranrommet

Intermembranrommet, commonly referred to in English as the mitochondrial intermembrane space, is the narrow compartment between the outer mitochondrial membrane and the inner mitochondrial membrane in most aerobic eukaryotic cells. It is bounded by these two membranes and lies within the organelle’s folded interior. The outer membrane is permeable to many small metabolites because of porins, while the inner membrane creates a highly selective boundary that helps define the environment of the intermembrane space. During cellular respiration, the electron transport chain pumps protons from the mitochondrial matrix into this space, making it slightly more acidic than the matrix and establishing the proton motive force used to drive ATP synthesis.

Contents and organization in the intermembrane space include small ions, metabolites in transit, and a set of proteins that participate in mitochondrial signaling and protein maturation. A key component is cytochrome c, which participates in electron transfer during respiration and, when released to the cytosol, acts as a trigger for apoptosis. The space also hosts enzymes and redox-active proteins involved in the maturation and maintenance of imported proteins. Many intermembrane space proteins are imported via specialized pathways, notably the Mia40/Erv1 (MIA) pathway, which assists in forming stabilizing disulfide bonds during protein folding.

Functions and significance: The intermembrane space contributes to energy production by supporting oxidative phosphorylation and maintains redox balance within the organelle. It also serves as a reservoir for signaling proteins that regulate cell fate; the controlled release of cytochrome c into the cytosol upon mitochondrial outer membrane permeabilization initiates apoptosis. Disruptions to the intermembrane space, its protein import systems, or its protein content can affect respiration, signaling, and cell survival.