Toxic effect of Ricinus lectin on XXXX cells in relation to enzyme modification of the cell surface.

@entity689 @entity157 @entity137 @entity3649
With regard to the toxic effects of Ricinus lectin, @entity689 -treated @entity157 cells have been found to be the most sensitive, and untreated @entity157 cells the least. Cells treated with @entity689 and @entity3649 oxidase exhibited an intermediate sensitivity. At 37 degrees C, the number of Ricinus lectin molecules bound to untreated, @entity689 -treated and @entity689 and @entity3649 oxidase-treated cells required to being about 30% @entity137 within 2 h was 15 . 10(5), 7.5 . 10(5) and 11.5 . 10(5) molecules/cell, respectively. This difference was rather small and suggests that the additional binding sites exposed following enzyme treatment were as efficient in mediating lectin @entity137 as those present before enzyme treatment. Positive cooperativity was observed during Ricinus lectin binding to enzyme-treated cells at 37 degrees C and the apparent association constant increased with the increase of binding site occupancy. The binding sites on enzyme-treated cells appeared to be homogeneous since under different physical conditions (4 degrees C) the shape of the Scatchard plot could be altered in such a way as to produce a single line of slope. In contrast to enzyme-treated cells, untreated cells did not exhibit a positive cooperative process either at 37 degrees C or at 4 degrees C. We found that the @entity137 of Ricinus lectin paralleled the irreversible specific binding of lectin, suggesting that only this was able to mediate the toxic effect. Our results are discussed in terms of the possible entry into the cells of Ricinus lectin and this occurs more rapidly in enzyme-treated than in untreated cells. This difference agrees with the sequence of events proposed: (i) Binding of Ricinus lectin; (ii) Clustering of lectin binding sites; and (iii) Endocytosis.
