The role of the high mannose carbohydrate chains in the mechanism of action of ricin toxin was investigated. Ricin is taken up by two routes in macrophages, by binding to cell surface mannose receptors, or by binding of the ricin galactose receptor to cell surface glycoproteins. Removal of carbohydrate from ricin by periodate oxidation led to a large loss in toxicity via both routes of uptake b...

Ricin is a potent toxin found in the beans of Ricinus communis and is often lethal for animals and humans when aerosolized or injected and causes significant morbidity and occasional death when ingested. Ricin has been proposed as a bioweapon because of its lethal properties, environmental stability, and accessibility. In oral intoxication, the process by which the toxin transits across intesti...

PURPOSE To examine force generation and duration of effect of botulinum toxin pretreatment, followed by injection of ricin-mAb35 in extraocular muscle. METHODS In normal adult rabbits, one superior rectus muscle was injected with either 5 units botulinum toxin or 1/50 maximally tolerated dose for rats (rMTD) of ricin-mAb35. Additional rabbits were first injected with 5 units botulinum toxin, ...

AB toxins such as ricin and cholera toxin (CT) consist of an enzymatic A domain and a receptor-binding B domain. After endocytosis of the surface-bound toxin, both ricin and CT are transported by vesicle carriers to the endoplasmic reticulum (ER). The A subunit then dissociates from its holotoxin, unfolds, and crosses the ER membrane to reach its cytosolic target. Since protein unfolding at phy...

As part of an effort to engineer ricin antitoxins and immunotherapies, we previously produced and characterized a collection of phage-displayed, heavy chain-only antibodies (VHHs) from alpacas that had been immunized with ricin antigens. In our initial screens, we identified nine VHHs directed against ricin toxin's binding subunit (RTB), but only one, JIZ-B7, had toxin-neutralizing activity. Li...

Depletion of intracellular K+ has been reported to result in an arrest of the formation of coated pits in human fibroblasts (Larkin, J.M., M.S. Brown, J.L. Goldstein, and R.G.W. Anderson, 1983, Cell, 33:273-285). We have studied the effects of K+ depletion on the cytotoxicities of ricin, Pseudomonas exotoxin A, and diphtheria toxin in Chinese hamster ovary (CHO) cells. The cytotoxicities of ric...

Seeds of the castor bean plant Ricinuscommunis L (CB) contain ricin toxin (RT), one of the most poisonous naturally-occurring substances known. Ricin toxin, a water-soluble glycoprotein that does not partition into the oil extract, is a ribosome-inactivating toxin composed of two chains, labeled A and B. Severity of the toxicity varies depending on the route of exposure to the toxin. Inhalation...

A hybrid protein of ricin and the enzymatically active fragment A of diphtheria toxin (toxin A) has been synthesized and purified. The diphtheria toxin A fragment of the hybrid protein is shown to enter the cytosol compartment of HeLa cells, its presence assayed by the fall of intracellular elongation factor II (EF-2) and the rise of ADP-ribosylated EF-2. Hybrid entrance to HeLa cells is blocke...

Diisopropylfiuorophosphate {OFP), a general serine protease inhibitor, inhibited the DNA fragme"tatioll and cell death in MDCK cells treated with ricin, modeccin, Ilseudomonas toxin, or dipbtberia toxin. Atrypsin-like serine protease inhibitor, IVLtosyl・L-lysine chleromethyl ketone (TLCK) also prevented ricin-induced DNA fragmentation and cel] death, albeit less effectiyely than DFP. Microscopi...

RTA, the catalytic A-subunit of the ribosome inactivating A/B toxin ricin, inhibits eukaryotic protein biosynthesis by depurination of 28S rRNA. Although cell surface binding of ricin holotoxin is mainly mediated through its B-subunit (RTB), sole application of RTA is also toxic, albeit to a significantly lower extent, suggesting alternative pathways for toxin uptake and transport. Since ricin ...