from
The Collaborative International Dictionary of English v.0.48
immunoglobulin \im`mu*no*glob"ulin\
([i^]m`m[-u]*n[-o]*gl[o^]b"[-u]*l[i^]n) n. (1953)
any one of a class of globular proteins which are antibodies
and are produced by the immune system in animals.
Note: The immunoglobulins form a series of related proteins
which are each composed of two pairs of polypeptide
chains, called heavy (H) and light (L, meaning of lower
molecular weight), all linked together by disulfide
bonds. They are subdivided on the basis of the
structural and antigenic properties of the H chains
into four subgroups, {immunoglobulin G} (IgG),
{immunoglobulin A} (IgA), {immunoglobulin M} (IgM), and
{immunoglobulin D} (IgD). They are divided also into
subclasses. Both H and L chains of anny given class and
subclass have regions which are of constant structure
within that class, as well as regions which are of
variable structure. The variable regions impart the
ability to recognize and bind to specific molecular
structures, thus providing the organism the capacity to
recognize and defend itself against the harmful effects
of substances foreign to the body. --Stedman
Syn: Ig.
[PJC]