Cellular membranes, specific recognition

Membranes play essential roies in the functions of both prokaryotic and eukaryotic cells. There is no unicellular or multicellular form of life that does not depend on one or more functional membranes. A number of viruses, the enveloped viruses, also have membranes. Cellular membranes are either known or suspected to be involved in numerous cellular functions, including the maintenance of permeability barriers, transmembrane potentials, active as well as specific passive transport across the membranes, hornione-receptor and transmitter-receptor responses, mitogenesis, and cell-cell recognition. The amount of descriptive material that might be included under the title of biological membranes is encyclopedic. The amount of material that relates or seeks to relate structure and function is less, but still large. For introductory references see Refs. 53, 38, 12, 47, 34, 13. Any survey of this field in the space and time available here is clearly out of the question. For the purposes of the present paper we have selected a rather narrow, specific topic, namely, the lateral diffusion of molecules in the plane of biological mem-branes.38,12,43,34 We consider this topic from the points of view of physical chemistry and immunochemistry. 

Subsequent to prenyl modification, Ras and most other CaaX proteins are further processed by two endoplasmic reticulum (ER)-localized, membrane-bound enzymes. The first prenyl-dependent processing step is the proteolytic removal of the -aaX tripeptide by the CaaX protease Reel this is followed by carboxymethylation of the now C-terminal prenylcysteine residue by the methyltransferase Icmt (Fig. 2). The result of these modifications is to produce a protein that exhibits some affinity for cellular membranes and also to impart a unique structure at the C-terminus that can serve as a specific recognition motif in certain protein-protein interactions. 

Selectins are a family of plasma membrane lectins that mediate cell-cell recognition and adhesion in a wide range of cellular processes. One such process is the movement of immune cells (T lymphocytes) through the capillary wall, from blood to tissues, at sites of infection or inflammation (Fig. 7-33). At an infection site, P-selectin on the surface of capillary endothelial cells interacts with a specific oligosaccharide of the glycoproteins of circu-... 

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