Human immunoglobulins are antibodies, according to eBioscience. They are derived from white blood cells and protect the body by binding to very specific antigens, such as those found on pathogens, and destroying them. There are two main types of antibodies: soluble antibodies and antibodies that are bound in a membrane.
Immunoglobulins are glycoproteins, which are made of a carbohydrate and a protein, according to MedicineNet. The five major isotypes are IgA, IgD, IgE, IgG and IgM, explains eBioscience. They can be told apart because the amino acids, which are molecules that go into the building of proteins, are arranged differently in the molecule's constant region. The constant region is an area where the amino acid sequence doesn't change, explains Dictionary.com. It determines the immunoglobulin's class and doesn't have contact with antigens.
These amino acid sequences are found in the heavy chains of the immunoglobulin, claims eBioscience. These are long chains of polypeptides. The immunoglobulins IgG and IgA are further broken down into subgroups because of small variations in the way the amino acids are arranged in their heavy chains. Immunoglobulins also have light chains, which are smaller chains of polypeptides. The two basic types of light chains are lambda and kappa, and each has its own constant and variable domains.