Toxins defined

This same experimental approach can be used to determine the appHcabiUty of the aDAS—AP to a competitive assay for DAS. As shown in Eigure 6, increasing amounts of free DAS were used to define the 50% inhibition level (ID q) of DAS for binding of two aDAS—AP conjugates to immobilized DAS. This approach was also used to determine the sensitivity of an EIA, as well as the specificity of the assay, as shown in Table 2. Increasing amounts of trichothecene mycotoxins closely related to DAS were added to microtiter plate wells containing a constant amount of prereacted DAS—aDAS—AP. After 30 min, excess toxin and any free toxin—aDAS—AP were washed out, and substrate was added. Quantification of the color produced was directly related to the abihty of the added toxin to displace aDAS—AP from the immobilized DAS, which is an indication that the aDAS also has an avidity for that toxin. 

Thus three lines of evidence define the rapidly dissociating receptor as the LR complex. Conditions known to uncouple R from G--first, guanine nucleotide and second, pertussis toxin—produce LR third, reconstitution of G protein restores receptor affinity, sensitivity to guanine nucleotide, and effector activation. In this sense, the ligand and binding behavior of this system is analogous to that of the beta-adrenergic receptor, where the LR and LRG complexes have already been studied with purified proteins and reconstituted membrane preparations (2,i0). 

Some Chemical Considerations Relevant to the Mouse Bioassay. Net toxicity, determined by mouse bioassay, has served as a traditional measure of toxin quantity and, despite the development of HPLC and other detection methods for the saxi-toxins, continues to be used. In this assay, as in most others, the molar specific potencies of the various saxitoxins differ, thus, net toxicity of a toxin sample with an undefined mixture of the saxitoxins can provide only a rough approximation of the net molar concentration. Still, to the extent that limits can be placed on variation in toxin composition, the mouse assay can in principle provide useful data on trends in net toxin concentration. However, the somewhat protean chemistry of the saxitoxins makes it difficult to define conditions under which the composition of a mixture of toxins will remain constant thus, attaining a reproducible level of mouse bioassay toxicity is difficult. It is therefore useful to review briefly some of the chemical factors that should be considered when employing the mouse bioassay for the saxitoxins or when interpreting results. Similar concepts will apply to other assays. 

The mouse bioassay for PSP, described in its original form by Sommer in 1937 (29), involves i.p. injection of a test solution, typically 1 mL, into a mouse weighing 17-23 g, and observing the time from injection to death. From the death time and mouse weight, the number of mouse units is obtained by reference to a standard table 1 mouse unit is defined as the amount of toxin that will kill a 20-g mouse in 15 min (77). The sensitivity of the mouse population used is calibrated using reference standard saxitoxin (70). In practice, the concentration of the test solution is adjusted to result in death times of approximately 6 min. Once the correct dilution has been established, 5 mice will generally provide a result differing by less than 20% from the true value at the 95% confidence level. The use of this method for the various saxitoxins and indeterminate mixtures of them would appear... 

Tetrodotoxin (TTX) and saxitoxin (STX) are potent sodium channel blockers that are found in phylogenetically diverse species of marine life. The wide distribution of TTX and STX has resulted in speculation that bacteria are the source of these toxins. Recently, investigators have reported isolation of marine bacteria, including Vibrio Alteromonas, Plesiomonas, and Pseudomonas species, that produce TTX and STX. This chapter details the methods and results of research to define bacterial sources of TTX and STX. 

In this scheme, EOH is the enzyme, IX is the inhibitor (either a carbamate or an organophosphate). EOH(IX) is analogous to the Michaelis Menton comploc seen with the substrate reaction. EOI is the acyl-enzyme intermediate for carbamates or a phosphoro-enzyme intermediate for the organophosphates. The equilibrium constant for this reaction (K ) is defined as k /k and the phosphorylation or carbamylation constant is defined as k2- In this study 42)y ANTX-A(S) was found to be more specific for AChE than BUChE. The double reciprocal and Dixon plot of the inhibition of electric eel AChE indicated that the toxin is a non-competitive inhibitor decreases, k remains unchanged) (Figure 2). 

Figure 1. Most cx)mmon (consensus) sequences of the two types of sea anemone toxins. Bold letters represent residues which both toxin types have in common. Letters above each sequence are nonconservative substitutions, while letters below each sequence are conservative substitutions. A nonconservative substitution was defined as one in which (a) electronic charge changed, (b) a hydrogen-bonding group was introduced or removed, (c) the molecular size of the sidechain was changed by at least 50%, or (d) the secondary structure propensity was changed drastically from b to h or vice versa (Ref.

Figure 2. Relative toxicity (LD50 and LD qq) estimates for actiniid sea anemone toxins upon crabs (Carcimis maenas) and mice. Values for Anemonia sulcata (As) and Anthopleura xanthogrammica (Ax) toxins are from ref. 24 data for Condylactis gigantea and Phyl-lactis flosculifera toxins are unpublished (Kem). The arrows indicate that the real mouse LD q values for Cg II and Pf II must exceed the values indicated in the Ogure. Although insufficient data are presently available to quantitatively define a relationship between mammalian and crustacean toxicity, it seems that there is usually an inverse relationship, which may be approximately defined by the stipple zone.

These structures show that RpII essentially consists of the small core of four-stranded )9-sheet and three relatively large loops. Residues 6-16, 23-30, and 35-40 form loops 1, 2, and 3, respectively, and the chain reversals are accomplished by tight turns involving residues D8-D11, E28-E31, and V36-P39. Segments involved in )5-sheet strands and loops alternate in the primary sequence of Rp toxins. As mentioned above, these structures indicate that the )5-sheet is highly twisted in order to form the correct disulfide bonds. Comparison of different refined structures of RpII indicate that the structure of loop 1 in RpII is less well defined than... 

In each of tiie assays of potency the amount of the immunosenim and the amount of a corresponding standard antitoxin dial are required to neutralize die effects of a defined dose of the corresponding toxin are determined. The two determined amounts and die assigned unitage of the standard antitoxin are dien used to calculate the potency of die immunoserum in International Units (lU). 

Choice of criteria for defining a "safe level of toxin In the environment based on animal and human observations ... 

HACCP is one of the minimum standards that is often required in a food processing enterprise to ensure that products do not contain harmful levels of biological, physical or chemical hazards such as pathogenic microorganisms or toxins. The overall idea of HACCP is to identify specific CCPs, which are those steps in the production process where the safety of the final product can be controlled most efficiently, and then define systematic procedures for monitoring and corrective action, to ensure that the risk is controlled at each... 

After all the answers from the interviews had been uploaded, an expert analysed each supply chain for each of the seven defined criteria for quality and safety microbial toxins and abiotic contaminants potential pathogens natural plant toxicants freshness and taste nutrient content and food additives fraud social and ethical aspects. For example, an expert on freshness and taste would check each major step in a supply chain for tomatoes to determine if it fulfilled the definition of a CCP (HACCP, Principle 2) in relation to freshness and taste for this commodity. If the step was considered to be a CCP, the answers in the questionnaire that related to relevant substeps at this step would be reviewed, to assess the control procedures that were in use for this CCP. The expert would then fill in the text field, structuring the input to consist of the following points ... 

J. P. Thompson and C.-L. Schengrund, Oligosaccharide-derivatized dendrimers Defined multivalent inhibitors of the adherence of the cholera toxin B subunit and the heat labile enterotoxin of E. coli to GM1, Glycoconjug. J., 14 (1997) 837-845. 

A randomized open trial, performed in patients with C. difficile pseudomembranous colitis, compared rifaximin (200 mg 3 times daily) to vancomycin (500 mg 2 times daily) and found the two drugs similarly effective [141]. The clearance of bacterial toxins was, however, more rapid with vancomycin. Further large double-blind clinical studies are needed to better define the role of rifaximin in the treatment of C. difficile infection. 

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