RESUMO
Multiple forms of ricin have been isolated from castor bean seeds. Two forms, ricin-1 and ricin-2, differ in their isoelectric pI values and toxicity towards IMR- 32 cells. Inhibition of IMR-32 DNA polymerase α2 is more pronounced with ricin-1 (65%) than with ricin-2 (10%). Ricin Β chain (pI = 5.2) isolated from ricin-1 binds to IMR-32 cell surfaces as well as inhibits DNA polymerase α2 activity when studied in vitro. The presence of galβ-linked glycoconjugates near the active site of IMR-32 DNA polymerase α2 has been proposed. Replication modulators which bind to the glycose portion of the enzymes involved in the replication system may need a mandatory binding to cell surface glycoconjugates for their activity.
RESUMO
232 mice were utilized in this study. ( 1 ) After administration of nitroquine 570mg/kg?1 po, the mice were given with normal saline(NS)and folic acid(NF,8 nag/kg x l im)in two subgroups respectively. 96h later, decrease in number and shorter in length of intestinal villi, and necrosis of epithelial cells, especially the crypt cells showed markedly in NS group, but much mild in NF group. ( 2 ) The DNA contents in the tissue of the small intestine showed decrease after nitroquine administration, & markedly in the larger dose and as the time going on. The values of cpm after the[3H] TdR incorporation into DNA wete much higher in NF group than in the NS group. The results suggest that the DNA synthesis in small intestine is promoted by folic acid, so that it is advantage for the repairing of damaged intestinal mucosa.