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Cell Wall and Cytoplasmic Isozymes of Radish -Fructosidase Have Different N-Linked Oligosaccharides

Laboratoire de Photobiologie—CNRS—LA203, Faculte des Sciences de Rouen, 76130 Mont Saint Aignan, France

When 36-hour-old dark grown radish seedlings are transferred to far-red light, there is a decrease in cytoplasmic -fructosidase (F) and an increase in cell wall F compared to the dark controls. Cytoplasmic and cell wall-bound -fructosidase are both glycoproteins and exhibit high antigenic similarities, but differ according to charge heterogeneity and carbohydrate microheterogeneity. Growth of radish seedlings in the presence of tunicamycin results in a partial inhibition of F glycosylation but nonglycosylated F still accumulates in the cell wall under far-red light. Thus, glycosylation is not necessary for intracellular transport, for correct targetting, or for wall association of an active F. The nonglycosylated cytoplasmic and cell wall F forms have the same relative molecular mass but glycosylated forms have different oligosaccharide side-chains, with respect to size and susceptibility to -mannosidase and endoglycosidase D digestion. The oligosaccharides of both forms are partly removed by endoglycosidase H when F is denatured. Isoelectric focusing analysis of F shows that the cell wall-associated isozymes are more basic than the cytoplasmic isozymes, and that the charge heterogeneity also exists within a single plant. A time course of changes in F zymograms shows a far red light stimulation of the appearance of the basic forms of the enzyme. However, the more basic cell wall specific F forms are not present when N-glycosylation is prevented with tunicamycin. These results indicate that cytoplasmic and cell wall F probably have common precursor polypeptides and basic cell wall forms arise via processing events which are tunicamycin sensitive.

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