JBC, Vol. 252, Issue 7, 2444-2446, Apr, 1977
Biosynthesis of lipid-linked oligosaccharides in cotton fibers. Stimulation by lipids from pig liver
W. T. Forsee and A. D. Elbein
An acidic lipid fraction isolated from pig liver (Forsee, W. T. &
Elbein, A.D. (1976) Proc. Natl. Acad. Sci. U.S.A. 73, 2574-2578) stimulated
the incorporation of mannose from GDP-[14C]mannose into lipid-linked
oligosaccharides using a particulate enzyme fraction from maturing cotton
bolls. This lipid fraction did not stimulate mannose incorporation into the
mannosylphosphorylpolyprenol. The 14C-oligosaccharides, formed in the
presence or absence of the pig liver "acceptor" lipid, were released from
the lipid-linked oligosaccharides by mild acid hydrolysis and were isolated
by paper chromatography. Both sets of 14C-oligosaccharides had similar
mobilities suggesting that they were qualitatively similar, except that
those formed in the presence of "acceptor" lipid had much more
radioactivity. The individual oligosaccharides were purified on a
calibrated column of Sephadex G-25 and were then subjected to various
treatments to obtain information about their structures. The molecular
weights of the larger oligosaccharides ranged from about L1210 to 1720
indicating they probably contained from 6 to 10 sugar residues. Strong acid
hydrolysis of the oligosaccharide with a molecular weight of 1350, followed
by reduction with NaB3H4, gave a ratio of [3H]hexitol to [3H]hexosaminitol
that was compatible with the molecular weight (about 5:2). However, the
hexitol fraction contained small amounts of [3H]glucitol in addition to
[3H]mannitol. Thus, this oligosaccharide may contain small amounts of
glucose in addition to mannose and GlcNAc. When the smaller
oligosaccharides (i.e. those having 5 or 6 sugars) were treated with
alpha-mannosidase, essentially of all the 14C was released as mannose, but
only 30 to 50% of the radioactivity could be released from the larger
oligosaccharides by this enzyme. Acetolysis of the oligosaccharide with a
molecular weight of 1720 released the radioactivity as mannobiose and
mannotriose suggesting that these oligosaccharides contain di- and
trisaccharide branches linked to the main chain in 1 leads to 6 linkages.