Ricin inhibitory effects

The inhibitory effect of ricin on protein synthesis in cell-free systems is greatly increased in the presence of / -mercaptoethanol. This is because free A chain is the enzymatically active toxin, whereas A chain linked to B chain in whole ricin is not active [ 121]. In the absence of reducing agents, even high concentrations of intact toxin do not inactivate ribosomes. Presumably the catalytic site on the A chain is formed or exposed only when the A chain is released from the B chain. Free A chain, however, is non-toxic to intact cells since, in the absence of B chain, it lacks the ability to bind to and enter cells. Ricin A-chain preparations frequently show some level of toxicity, however, because the complete removal of contaminating B chain can be difficult to achieve [ 122]. 

To detect ricin, we studied its inhibitory effects on luciferase expression by adding a series of concentrations of ricin into the IVT reactions in the array device. To achieve a lower detection limit, 4-hr protein expression was used, though ricin detection can be achieved in as short as 5 minutes. Ricin sample size was 2 pL. As shown in Figure 5a, the expression yield of luciferase, indicated by luminescence, decreases with the concentration of ricin (solid circles). However, the expression yield remained the same when the ricin is heat denatured and its toxicity is deactivated (open circles). The error bar of each data point indicates the standard deviation that is obtained from three repeat experiments. The calibration curve is obtained by plotting the detection... 

Figure 5 (a) The inhibitory effects of ricin on the production yield of luciferase. The expression yield of luciferase is plotted as a function of the concentration of ricin (solid circles) and heat-denatured ricin (open circles), (b) Calibration curve for ricin detection. (Reproducedfrom reference 14. Copyright 2006American Chemical Society)... 

Ricin - A phytotoxic protein from Ricinus communis is inhibitory towards protein synthesis in experimental tumor cells. It has a moderate Inhibitory effect on DNA synthesis without affecting RNA synthesis. Its mode of action is not known, but is not due to impairment of glucose metabolism nor amino acid uptake in tumor cells.173... 

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