The formation of oligoglucans linked to lipid during synthesis of β-glucan by characterized membrane fractions isolated from peas

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Abstract
Membrane fractions were obtained from peas roots by using a method that permitted the isolation of a fraction rich in relatively intact dictyosome stacks. No chemical fixatives were used. The method involved incubation of the roots with cellulase, followed by gentle homogenization and sucrose-density-gradient fractionation of the homogenate. The fractions were characterized by electron microscopy. All fractions were enzymically active in incorporating glucose from UDP-glucose into water-insoluble glycolipids containing both single glucose residues and glucose oligosaccharides. Some or all of the linkages of glucose to lipid were through phosphate esters. A substance containing glucose oligosaccharides attached to or very strongly adsorbed on to protein was also formed. The membrane fractions also incorporated glucose from UDP-glucose into alkali-soluble and alkali-insoluble β-glucans, which like the oligosaccharides contained β(1leads to 3) and β-(1leads to4) linkages. The distribution of the enzymic activities and the chemical properties of the lipid-linked and protein-linked oligosaccharides suggest that they may be intermediates in β-glucan synthesis. The synthetic activity is associated with smooth-membrane vesicles which may be derived from the plasma membrane.