membranesidan

Membranesidan, literally “the membrane side” in Swedish, is a term used in biology to describe the surface of a biological or artificial membrane that faces a particular compartment, such as the cytoplasm or the extracellular space. It denotes orientation and side-specific phenomena that can influence how molecules interact with the membrane.

In a phospholipid bilayer, the two leaflets can have different lipid compositions and protein orientations. The membranesidan facing the cytoplasm contains cytosol-facing domains of membrane proteins and specific lipids, while the opposite side faces the extracellular milieu. This membrane asymmetry is important for processes such as signal transduction, membrane trafficking, and the localization of certain enzymes and receptors.

In experimental and methodological contexts, the term is used to specify which side of a membrane is involved in interactions, for example in protein reconstitution experiments, transporter activity assays, or binding studies. Clarifying the membranesidan helps interpret data on side-specific transport, gating, or cytosolic versus extracellular signaling.

The term is more common in Swedish-language literature and is less frequently used in English. It remains a descriptive concept rather than a formal classification, employed to convey orientation and interactions at the interface of the membrane.

See also: lipid bilayer, membrane asymmetry, flip-flop, transport proteins, planar lipid bilayers.