Three lectins have been isolated from an extract of mistletoe (Viscum album) by affinity chromatography on partially hydrolysed Sepharose and human immunoglobulin- Sepharose. The lectins differ in molecular weight and sugar specificity (lectin I, mol.wt. 11500, D-galactose-specific; lectin II, mol.wt. 60000, both D-galactose- and N-acetyl-D-galactosamine-specific; lectin III, mol. wt. 50000, N-acetyl-D-galactosamine-specific). All three lectins react with human erythrocytes without specificity for the A, B, and O blood groups. In contrast with abrin and ricin the mistletoe lectins cannot be divided into "toxins" and "haemagglutinins".

A comparative study was carried out on the effect of viscotoxin and mistletoe lectin I, two mistletoe proteins known to be toxic to mammals, on three tumour cell lines in culture (Yoshida sarcoma cells, T-cell leukaemia cells Molt4, and myeloid cells K562). Both viscotoxin and mistletoe lectin were cytotoxic for the three cell lines tested, although the cell sensitivity was dependent on the type of cells used. Yoshida cells were the most sensitive to viscotoxin (EDSo=0.7 pg/mL) and less sensitive to mistletoe lectin (EDSo= 12.8 pg/mL). K562 cells were more sensitive to mistletoe lectin (EDSo=75 pg/mL) than Molt4 cells (EDSo= 1.3 ng/mL), whose high sensitivity to mistletoe lectin is well known. Data are also reported showing that this cell line dependent sensitivity can be exploited to demonstrate and/or to discriminate the toxic activities of either substances in crude mistletoe extracts. In particular the Yoshida cell line can represent a suitable system for a bioassay of viscotoxin in these extracts.

1. The haemagglutinating and toxic lectin from Viscum album L. (mistletoe) inhibits protein synthesis in a lysate of rabbit reticulocytes, with an ID50 (concentration giving 50% inhibition) of 2.6 microgram/ml. This effect is enhanced (ID50 0.21 microgram/ml) if the lectin is reduced with 2-mercaptoethanol. 2. The lectin inhibits protein synthesis also in BL8L cells in culture. Inhibition occurs after a lag time of 3 h. The ID50 is 7 ng/ml, and increases after reduction of the lectin. 3. This and the gross lesions observed in rats poisoned with V. album lectin indicate this is a toxin very similar to ricin.

A lectin from Viscum album which specifically binds to D-galactose was isolated by affinity chromatography on O-lactosyl-, O-galactosyl-polycarylamide or hydrolized sepharose 4 B. Some serological and physicochemical properties of the agglutination are reported.

No abstract