Biosynthesis of pulmonary glycoconjugates--V. Biosynthesis of oligosaccharide inner core region of N-glycoprotein in lung microsomes.

Lung microsomes are able to synthesize dolichyl-mannosyl-phosphate, which stimulates the biosynthesis of a product (P1), soluble in chloroform/methanol/water (10:10:3, v/v). In presence of pulmonary dolichyl-mannosyl-phosphate, liver microsomes synthesized 3 mannosylated products: X1 product recovered in chloroform/methanol extract, X2 and X3 products soluble in chloroform/methanol/water (10:10:3, v/v). Mild acid hydrolysis of P1 product released one mannosylated oligosaccharide which remained at the origin in our solvent system, since two mannosylated oligosaccharides, released from products synthesized in liver, moved very slowly. Addition of N,N'-diacetyl [14C]chitobiosyl-pyrophosphoryl-dolichol to lung microsomes incubated with GDP-[3H]mannose stimulated the synthesis of a [3H, 14C]product extracted with chloroform/methanol (2:1, v/v). Mild acid hydrolysis of this product released [3H, 14C]oligosaccharide which moved very slowly on paper chromatography, in our solvent system. These results demonstrate that lung tissue can synthesize the oligosaccharide inner core region of N-glycoprotein with the sequence (Man)x-(GlcNac)2. But pulmonary dolichol pool is probably involved in other lipid biosynthesis pathways.