Golgi-associated processing of complex-type oligosaccharides linked
to asparagine involves the sequential action of at least six enzymes.
By equilibrium sucrose density gradient centrifugation of membranes
from Chinese hamster ovary cells, we have partially resolved the
set of four initial enzymes in the pathway (Mannosidase I, N-acetylglucosamine
(GlcNAc) Transferase I, Mannosidase II, and GlcNAc Transferase II)
from two later-acting activities (galactosyltransferase and sialyltransferase).
In view of the recent demonstration that galactosyltransferase is
restricted to the trans face of the Golgi complex in HeLa cells (Roth,
J., and E.G. Berger, 1982, J. Cell Biol., 93:223-229), our results
suggest that removal of mannose and attachment of peripheral N-acetylglucosamine
may occur in some or all of the remaining cisternae on the cis side
of the Golgi stack.
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