1. Dianthin 30 and dianthin 32, two proteins isolated from the leaves of Diathus caryophyllus (carnation), were purified to homogeneity by chromatography on CM-cellulose. 2. The mol.wt. of dianthin 30 is 29 500 and that of dianthin 32 is 31 700. Both dianthins are glycoproteins containing mannose. 3. Dianthins inhibit protein synthesis in a lysate of rabbit reticulocytes, with an ID50 (concentration giving 50% inhibition) of 9.15 ng/ml (dianthin 30) and 3.6 ng/ml (dianthin 32). They act by damaging ribosomes in a less-than-equimolar ratio. Protein synthesis by intact cells is partially inhibited by dianthins at a concentration of 100 microgram/ml. 4. Dianthins mixed with tobacco-mosaic virus strongly decrease the number of local lesions on leaves of Nicotiana glutinosa.

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.

Two epithelial cell lines have been derived from rat liver. One, containing only low levels of gamma-glutamyl transferase (GGT) was obtained from normal liver and the other, containing high levels of the enzyme was isolated from an aflatoxin B1-induced hepatoma. The GGT levels present in the two cell lines have been examined by histochemical staining, by a fluorescence assay using disrupted cells, and also by intact fluorescence-labelled cells in a laser flow cytofluorimeter. The cells containing high levels of GGT have been found to be less sensitive to microsomally-activated aflatoxin B1 than are the GGT negative cells, a feature of the in vivo situation. Evidence for activation of the gamma-glutamyl derivative of an alkylating mustard analogue of p-phenylene diamine by the GGT positive cells is presented. This finding could be of relevance to the possible chemotherapy of GGT-rich lesions in vivo.

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