intermembrana

Intermembrane space refers to the narrow region between the inner and outer membranes of certain double-membrane organelles, most notably mitochondria and chloroplasts. In mitochondria, this space lies between the outer mitochondrial membrane and the inner mitochondrial membrane. It plays a key role in bioenergetics and signaling: during respiration, protons are pumped across the inner membrane and accumulate in the intermembrane space, helping to establish the proton motive force used by ATP synthase as protons flow back into the matrix. The intermembrane space also houses soluble proteins involved in electron transport and stress responses, including cytochrome c.

Cytochrome c, a central component of the electron transport chain, resides in the intermembrane space and can be released into the cytosol when the outer membrane becomes permeable, a step in the activation of apoptotic pathways. The intermembrane space also contains proteins involved in the import and oxidative folding of IMS proteins, notably through the mitochondrial intermembrane space assembly (MIA) pathway, which includes components such as Mia40 and Erv1 that catalyze disulfide bond formation.

In chloroplasts, a comparable intermembrane space exists between the outer and inner envelope membranes. This space participates in metabolite exchange and supports the import of nuclear-encoded proteins into the chloroplast, in conjunction with the Toc and Tic translocon systems that span the outer and inner membranes.

Overall, the intermembrane space is a dynamic compartment essential for energy conversion, protein quality control, signal transduction, and apoptosis, with variations in composition reflecting the specific needs of different organelles.