Ricin inactivation

The way in which ricin inactivates ribosomes was first described by Endo and Tsurugi (1987) who showed that RTA cleaves a single specific gly-cosidic bond within the large ribosomal RNA (rRNA) of the 60S subunit of eukaryotic ribosomes. RTA must be separated from RTB to display this activity (Lewis and Youle, 1986 Wright and Robertus, 1987). The glycosidic bond is that of a specific adenine nucleotide that lies in a universally conserved sequence of 12 nucleotides, 5 - A G l J A C G A G A G G A - 3 (target adenine... 

The toxins or-sarcin and ricin inactivate ribosomes by altering a highly conserved sequence in 23S-like rRNAs (the sarcin-ricin loop). Elongation factors Tu and G bind near this loop, suggesting that it is involved in AA-tRNA selection and translocation. Protein L6 and the sarcin-ricin loop are involved in translational accuracy control, as suggested by the mutations in these components that... 

Ricin, an extremely toxic molecule isolated from the castor bean, inactivates eukaryotic 28S tibosomal RNA by providing the N-glycolytic cleavage or removal of a single adenine. 

Due to the extraordinary toxicity of intact ribosome-inactivating toxins like ricin, abrin, and modeccin, purification and handling of these proteins must be done with extreme care. Even dust from crude seed powders or lyophilized proteins should be considered dangerous. During... 

Delayed-action cytotoxin that inhibits protein synthesis (ribosomal inactivating protein) that is obtained from castor beans (Ricinus communis). Waste from production of castor oil contains about 5% ricin by weight. It is a white powder that is soluble in water and relatively heat stable. Aqueous solutions are resistant to chlorine at 10 ppm. It is persistent in the environment. 

Highly potent bacterial toxins such as ricin and diphtheria can completely inhibit cellular protein synthesis at very low levels [26]. The bacterial toxin exerts cytotoxicity through enzymatic inactivation of factors essential for protein synthesis (e.g., riboso-mal RNA, elongation factor 2 or EF2). Inactivation of these proteins, which are... 

Several other inhibitors of protein synthesis are notable because of their toxicity to humans and other mammals. Diphtheria toxin (Mr 58,330) catalyzes the ADP-ribosylation of a diphthamide (a modified histidine) residue of eukaryotic elongation factor eEF2, thereby inactivating it. Ricin (Afr 29,895), an extremely toxic protein of the castor bean, inactivates the 60S subunit of eukaryotic ribosomes by depurinating a specific adenosine in 23S rRNA. 

Endo, Y. (1988) Mechanism of action of ricin and related toxins on the inactivation of eukaryotic ribosomes, in Immunotoxins (Frankel, A. E., ed.), Kluwer Academic, Boston, pp. 75—89. 

Ricin can be made from the waste material left over from processing castor oil. It can be made in either powder, mist, or pellet form, or it can be dissolved in water or weak acid. Ricin is a stable substance under normal conditions, but can be inactivated by heat above 80°C. 

Abrin exerts its toxic action in the same way as ricin. The abrin B-chain avidly binds to a variety of cell types, in particular reticuloendothehal cells which bear the appropriate mannose receptors. The abrin B-chain also binds to the galactosyl-terminated receptors on the cell membrane to allow the entry of the abrin A-chain. Once internalized, the abrin A-chain is transported from the cell membrane to the ribosomes, where it catalytically inactivates the 60S ribosomal subunit by removing adenine from positions 4 and 324 of 28S rRNA, thereby inhibiting protein synthesis and causing cell death (Stripe and Barbieri, 1986). 

Goat 5g Age of ruminant can be a factor as the rumen may inactivate ricin... 

Ricin is a lectin-type globular glycoprotein and consists of A and B chains (Doan, 2004 Li and Pestka, 2008). Ricin is considered a Type 2 ribosome-inactivating protein (RIP) (Millard and LeClaire, 2008). The ricin B chain attaches to the plasma membrane at the galactose receptors, pits are... 

Jackson, T.F., Halbert, F.L. (2006). Thermal inactivation of ricin using infant formula as a food matrix. J. Agric. Food Chem. 54 7300. ... 

Fig. 3.3 shows the principle behind the design of immunotoxins. A number of protein toxins of bacterial and plant origin are useful for the production of immunotoxins. These include the diphtheria toxin and pseudomonas exotoxin from bacteria, and ricin, arbin, pokeweed antiviral proteins, saporin, and gelonin from plants (Pastan et al, 1986 Pastan and FitzGerald, 1991). All of these toxins kill cells by entering the cells, and enzymatically inactivating the translational machinery of the cells. Some, such as diphtheria toxin, arbin, and ricin, are composed of two protein chains, A and B. The B chains bind to the cell-surface... 

Ricin cleaves a single adenine from 28S rRNA and inactivates the 60S ribosomal subunit. One molecule can kill an entire cell. 

Two commercial vaccines based on virosome technology are currendy on the market. Epaxal (Berna Biotech Ltd, Bern, Switzerland), a hepatitis A vaccine, has inactivated hepatitis A virus particles adsorbed on the surface of the immunopotentiating reconstituted influenza virosomes (IRIV). In Inflexal V (Berna Biotech Ltd) the virosome components themselves are the vaccine protective antigens (185). Recently, in phase I study liposome-encapsulated malaria vaccine (containing monophosphoryl lipid A as adjuvant in the bilayer), the formulation showed induction of higher level of anti-malaria antibody in human volunteers (186). Some liposomal formulations are under investigation in preclinical studies against Yersina pestis, ricin toxin and Ebola Zaire virus (77, 187). 

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