In the periplasmic space of Gram negative bacteria proteins exist that specifically bind different substances. They are characterized by a uniform plan for the construction and operation model. They serve as receptors in the primary transport across the cell membrane-bound ligands themselves. Cooperate with ABC transporters, transport systems widespread in both prokaryotes as well as in eukaryotes. Furthermore, they have additional features: Molecular piastunek caring for periplasmic proteins, and primary process chemotaxis receptors.