Cell membranes glycosylphosphatidyl inositol

FIGURE 7-1 The immunoglobulin (Ig) gene family of molecules. Several varieties of Ig domain-containing molecules are contained within the Ig gene superfamily. Most are type I membrane proteins some have only Ig domains or other moieties that may convey function (see text). V, variable Ig domain C, constant Ig domain MAG, myelin-associated glycoprotein NCAM, neural cell adhesion molecule GPI, glycosylphosphatidyl-inositol EC, extracellular domain FN, fibronectin. 

Glycosylphosphatidyl inositol anchors constitute a class of glycolipids that link proteins and glycoproteins via their C-terminus to eukaryotic cell membranes. The first structure of a GPI anchor, that of Trypanosoma brucei, was published by Ferguson et al. [262]. Since then quite a few examples of GPI anchors were described, allowing the definition of the core structure depicted inO Scheme 37 [263]. 

The ubiquitous existence of folate receptor in mammalian cells, tissues and body fluids is now well-established. Folate receptor occurs in isoforms equipped with a hydrophobic glycosylphosphatidyl inositol tail enabling anchorage to plasma membranes. The RFCl, which is an anion exchanger, has the properties of a classical facilitative carrier with high affinity for reduced folates. The 5-CH3-THF is taken up by the folate receptor with high affinity (.K = 1-10 nM) (Table 44.3) and by the RFC with relatively low affinity (.K = 1-10 pM). 

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