Cell-free labeling in thyroid rough microsomes of lipid-linked and protein-linked oligosaccharides: I. Mannosylated units |
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Authors: | Catherine Ronin Simone Bouchilloux |
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Institution: | Laboratoire de Biochimie Médicale, Faculté de Médecine, Bd. J. Moulin, 13385 Marseille, Cedex 4 France |
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Abstract: | In order to evaluate the possibility in a pig thyroid rough microsomal system of a transfer of pre-assembled sugar cores from sugar-lipids to protein, we have examined after incubation with GDP-14C]Man the compounds bearing labeled saccharides and have determined some properties of their released saccharide moieties. The 14C]Man material specifically soluble in CHCl3/CH3OH/H2O, 10 : 10 : 3, behaved on DEAE-cellulose and when treated with hot alkali and alkaline phosphatase as a lipid pyrophosphate (sometimes accompanied by some ). Its saccharide moiety, released by mild acid, exhibited properties (molecular size, sensitivity to α-mannosidase, affinity for concanavalin A and charge modification introduced by a strong reductive alkaline treatment) pointing to a polymannosylated N,N′-diacetylchitobiose containing an average of nine monosaccharide units (from six to twelve). The 14C]mannosylated glycoproteins have represented all the polymeric label remaining after lipid extraction. From the susceptibility of their pronase glycopeptides to a differential reductive alkaline hydrolysis, it was concluded that their label belonged mainly to N-glycosidically linked units. Released saccharides exhibited the same properties as those from lipids, a result substantiating the possibility raised from previous studies of a transfer of pre-assembled moieties. |
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