Studies on the anti-mitogenic, anti-phage and hypotensive effects of several ribosome inactivating proteins.

An investigation was conducted to compare the anti-mitogenic, anti-phage and hypotensive activities of several ribosome inactivating proteins (RIPs) in order to ascertain whether the RIPs differed in their potencies in the various bioassays. Agrostin, luffin and saporin elicited a dose-dependent suppression of the mitogenic response of murine splenocytes to concanavalin A. The three RIPs were approximately equipotent in this regard, with near maximal inhibition attained at a dose of 83 nM and approximately 50% inhibition at 830 pM. Trichosanthin was slightly more potent than the three aforementioned RIPs. All of these RIPs were capable of inhibiting the replication of phage M13 in the bacterium Escherichia coli, the ranking of potencies being luffin>trichosanthin>agrostin when tested at a concentration of 3.5 microM. The RIPs gelonin and saporin did not exert a conspicuous antiviral effect at the same dose. After intravenous administration into normotensive rats via the external jugular vein, the RIPs saporin, trichosanthin, gelonin and momordin evoked a mild hypotensive response while luffin and agrostin were inactive. The hypotensive response, however, lacked dose dependence. The RIPs trichosanthin, momordin and gelonin did not affect the blood pressure response to angiotensin I. Chemical modification of the arginine residues of the RIPs brought about a reduction in their ability to inhibit cell-free translation. It appears that the ranking of potency of RIPs in one bioassay was different from the rankings in other assays.