Involvement of Lipid-linked Oligosaccharides in Synthesis of Storage Glycoproteins in Soybean Seeds

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Abstract
Membrane preparations from developing soybean (cv. Prize) cotyledon tissue, at the time of synthesis of storage glycoproteins, catalyze the sequential assembly of lipid-linked oligosaccharides from uridine-5''-diphospho-N-acetyl-D-[6-3H]glucosamine and guanosine-5''-diphospho-D-[U-14C]mannose. The maximum size of lipid-linked oligosaccharide that accumulates contains the equivalent of 10 saccharide units on the basis of Bio-Gel P-2 gel filtration studies. These lipid-linked oligosaccharides show similar characteristics to polyisoprenyl diphosphate derivatives on diethylaminoethyl-cellulose chromatography and are potential intermediates in glycoprotein biosynthesis in this tissue. These glycolipids do not appear to turn over in pulse-chase experiments and no completed storage glycoproteins were detected among the products of these incubations. Tissue slices from cotyledons at the same stage of development synthesize lipid-linked oligosaccharides from [3H]mannose and [3H]glucosamine with sizes equivalent to 1, 7, 10 and .apprx. 15 saccharide units. In pulse-chase experiments, the lipid-linked saccharides with the equivalent of 1 and 10 units rapidly turn over, whereas those with 7 and 15 units do not. Examination of the higher oligosaccharide peaks (10 and 15) by gel filtration shows them to comprise 2 distinct subsets of oligosaccharides containing different proportions of glucosamine and mannose units. Tissue slices synthesize products which resemble the completed 7S storage glycoproteins as judged by similarity of molecular weight and precipitation with specific antisera. Analysis of the oligosaccharides obtained by hydrazinolysis of glycoproteins shows the presence of a similar size high-mannose type N-linked oligosaccharides as in other glycoproteins from animal and plant cells.