Biochemical Techniques and Instrumentation

2.4.3. Types of ligands

There are different molecules that can be used as specific ligands based on their specific or reversible binding properties. Important ligands include proteins, nucleic acids , lectins and textile dyes.

1. Proteins : Protein ligands include immobilized enzymes, coenzymes, antibodies, antigens, proteins and hormones. Immobilized enzymes are used to isolate both coenzymes and substances. Proteins ligands such as Protein A, Protein G, avidin and streptavidin are used to isolate monoclonal antibodies from cell cultures and for the isolation of biotin-labelled molecules. Immobilized hormones are used to isolate specific receptors as peptide antigens.

2. Nucleic Acids: DNA and RNA are used as immobilized ligands for the isolation of proteins which specifically bind to nucleic acids.

3. Lectins: Lectin, a plant protein has strong affinity to bind certain carbohydrate residues. eg. Concanavalin A

4. Textile Dyes: Synthetic textile dyes with a wide variety of biological materials are used as affinity ligands. They are suitable for the isolation of lipoproteins, α-fetoprotein, IgG, α₂-macroglobulin and human clotting factors. eg. Cibacron Blue

Table 2.4.3. gives the types of ligands and their specific affintity towards different molecules.