Antigens hydrophobic moiety

Glycoproteins play major roles in antigen-antibody reactions, hormone function, enzyme catalysis, and cell-cell interactions. Membrane glycoproteins have domains of hydrophilic and hydrophobic sequences and are amphi-pathic molecules. The carbohydrate moieties of glycoproteins are distributed asymmetrically in cell membranes, cluster near one end of the protein molecule (Figure 10-7), and constitute a hydrophilic domain of amino acid residues (Chapter 21) as well as carbohydrates. The hydrophobic domain of the molecule interacts with the lipid bilayer. 

One new approach that is being developed to enhance tumour specificity used monoclonal antibodies (mAb), raised against a particular type of tumour, as a kind of molecular "guided missile", with a porphyrin attached to the mAb as the light-activated "warhead." Tumour cells have different surface antigens to normal cells, and it is possible to raise mAbs specific for these antigens. Tumour cells also differ from normal cells in that they express a large number of low-density lipoprotein receptors. Hydrophobic photosensitisers may then be incorporated into a lipid moiety of such a receptor, and taken into the tumour cell via lysosomes. 

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