57
was to incubate the purified cells in only the secondary
antibody since rapid turnover of the antigen did not seem
to occur.
As was stated earlier, the antigen recognized by A2B5
is a ganglioside (Eisenbarth et al., 1979; Kasai and Yu,
1983). These sialoglycosphingolipids are believed to be
synthesized in an progressive fashion from individual
sugars transfered from nucleotide conjugates (Ledeen,
1985). This apparently takes place in the Golgi apparatus
and probably the smooth endoplasmic reticulum through
membrane bound multienzyme complexes specific for synthesis
of each ganglioside. This occurs only in the cell soma of
neurons in the chick visual system (Landa et al., 1979)
after which the gangliosides translocate to nerve endings
via fast axonal transport (Ledeen, 1985). In fractionated
cells gangliosides are found predominantly in the
synaptosomal and microsomal fractions (Hamberger and
Svennerholm, 1971). Gangliosides exhibit turnover and are
degraded primarily in lysosomes in an ordered fashion and
evidence suggests that postsynthetic processing of them
does not occur (on the cell surface) between synthesis and
degradation (Ledeen, 1985).
The mechanisms that control the synthesis and export
of gangliosides to the cell surface not at nerve endings
are not well understood. From what is known about
ganglioside biosynthesis (Ledeen, 1985) it is probable that