(PROTEIN) WATER MOLECULE AMINO GROUP

254 • Biochemistry of the Eye
Figure 9–5
A radioimmunoassay combines the sensitivities of both radioactive and immunochemical
reactions. ➤ In the assay, a radioactive antigen competes with a nonradioactive
antigen for the possession of a binding site on an antibody. The assay
ultimately measures the radioactivity on the bound antibody. Accordingly, the
greater the binding of a nonradioactive antigen on an antibody, the lower the level
of radioactivity measured. The control gives the reference radioactivity for 100%
binding of radioactive antigen. In the assay, standard, known amounts of nonradioactive
antigens are reacted in the upper row and compared with the control.
From this, a standard curve is constructed (shown on right). One or more
unknown samples are run. The percent of radioactivity in the antibodies are
measured and intersected with the standard curve to obtain the concentration of
antigen. This method, for example, is very useful in determining very low concentrations
of hormones present in blood.
partially understood (Hay and Westwood, 1998). As mentioned, B cells
or B lymphocytes are the site of immunoglobulin synthesis. In the adult
human, B cells are formed in the bone marrow and then transported to
lymphoid tissues prior to full development as B plasma cells. When they
leave the bone marrow they can only produce nonspecific IgM and IgD
that binds to the cell surface membrane at the stem side of the molecule
(Banchereau and Rousset, 1992). In the lymphoid tissues, the B cells are
induced to make specific immunoglobulins by the binding of antigens to
TABLE 9–2 ➤
FACTORS THAT CONTRIBUTE TO ANTIGEN-
ANTIBODY REACTIONS AT THE ANTIGEN-BINDING
REGION OF AN IMMUNOGLOBULIN
Factor Type Characteristic
Chemical bond Hydrogen Sharing of a hydrogen atom due to partial
charges between two atoms
Electrostatic Full positive and/or negative charge(s) on
antigen and/or antibody, respectively
van der Waals Induced partial charge between two atoms
(not involving hydrogen)
Nonpolar bond Hydrophobic Association of molecules away from a
water (polar) environment
Conformation Lock and key Complementary shape of antigen and
hypervariable part of V domain