472
JOHN E. CUSHING
C. The yM Molecule
It will be recalled that this molecule consists of a complex of five
subunits, and it is therefore considerably larger than yG. Each single
subunit is constructed very much like yG, consisting of two L and two
H chains of the same relative lengths. The “same” L chains that occur
in yG are used in constructing this molecule even to the point of showing either the K or h specificities. However, while of comparable length,
the H chains used show a single unique antigenic specificity (designated
p ) , in contrast to the four possible yG, which helps to characterize this
class of globulin, Allotypes have not yet been demonstrated in the $4
molecules.
This class of Ig appears first during the ontogenetic development
of immunological competence, and also first, in subsequent life, during
a course of immunizations; ,M antibodies also have a more efficient
hemolytic relationship with complement than do yG and exhibit other
differences in immunological relations.
D. The Primary Amino Acid Sequences
of L and H Chains
It is well known that only a small percentage of the surface of the
intact antibody molecule is devoted to forming a combining site and
that the yG molecule has two such sites, both of which appear to be
identical in any one molecule with respect to their specific afl3nity for
antigen. It is also well known that a population of antibody molecules
having affinity for a given antigenic specificity shows great heterogeneity, not only of the sort already reviewed in preceding sections
but also at the site itself as measured by degree of affinity and specificity.
This variability is imposed upon the more general heterogeneity to the
point that essentially an “infinite” number of antigenic specificities can
be recognized by the antibody synthesizing machinery. This capacity
for recognition is the basis for considering the synthesis of antibody as
the most unique and remarkable protein synthesis known. Immunochemists are devoting much effort to the determination of the molecular
architecture of Ig molecules with the aim of learning how the remarkable properties of the combining site are contrived. These studies are
still in progress and rapidly evolving. However, some concepts are
emerging that will be considered here, again largely with reference to
the yG molecule.
JOHN E. CUSHING
C. The yM Molecule
It will be recalled that this molecule consists of a complex of five
subunits, and it is therefore considerably larger than yG. Each single
subunit is constructed very much like yG, consisting of two L and two
H chains of the same relative lengths. The “same” L chains that occur
in yG are used in constructing this molecule even to the point of showing either the K or h specificities. However, while of comparable length,
the H chains used show a single unique antigenic specificity (designated
p ) , in contrast to the four possible yG, which helps to characterize this
class of globulin, Allotypes have not yet been demonstrated in the $4
molecules.
This class of Ig appears first during the ontogenetic development
of immunological competence, and also first, in subsequent life, during
a course of immunizations; ,M antibodies also have a more efficient
hemolytic relationship with complement than do yG and exhibit other
differences in immunological relations.
D. The Primary Amino Acid Sequences
of L and H Chains
It is well known that only a small percentage of the surface of the
intact antibody molecule is devoted to forming a combining site and
that the yG molecule has two such sites, both of which appear to be
identical in any one molecule with respect to their specific afl3nity for
antigen. It is also well known that a population of antibody molecules
having affinity for a given antigenic specificity shows great heterogeneity, not only of the sort already reviewed in preceding sections
but also at the site itself as measured by degree of affinity and specificity.
This variability is imposed upon the more general heterogeneity to the
point that essentially an “infinite” number of antigenic specificities can
be recognized by the antibody synthesizing machinery. This capacity
for recognition is the basis for considering the synthesis of antibody as
the most unique and remarkable protein synthesis known. Immunochemists are devoting much effort to the determination of the molecular
architecture of Ig molecules with the aim of learning how the remarkable properties of the combining site are contrived. These studies are
still in progress and rapidly evolving. However, some concepts are
emerging that will be considered here, again largely with reference to
the yG molecule.