Välismembranen

Välismembranen is a term used in cell biology to describe the region that lies between two lipid bilayers enclosing an intracellular compartment. In many contexts, it is most familiar as the intermembrane space—the space between the outer and inner membranes of mitochondria—and, in chloroplasts, the space between their outer and inner envelope membranes.

These intermembrane regions are bounded by phospholipid bilayers and contain a specific mix of ions, small solutes, and proteins that regulate transport and signaling. In mitochondria, the intermembrane space hosts components of the electron transport chain and, under certain conditions, proteins such as cytochrome c that can be released into the cytosol to trigger programmed cell death. In chloroplasts, the intermembrane space participates in the transport of metabolites between the outer envelope and the internal compartments of the organelle.

Functions commonly associated with the välismembranen include helping to establish and maintain ion gradients across membranes, supporting the function of transporters and translocons that move proteins and metabolites, and serving as a site for signaling events. The composition of these spaces is dynamic and can change in response to cellular energy needs, stress, and developmental cues. In animal cells, disruptions to the intermembrane space can have implications for apoptosis and cellular homeostasis.

In terminology, the term välismembranen is encountered primarily in Swedish-language literature as a general label for the intermembrane region of organelles such as mitochondria and chloroplasts. In other languages, the corresponding term is usually intermembrane space or intermembrane region.