Toxin precursors

This calcium-ion-activated enzyme [EC 3.4.21.61] catalyzes the hydrolysis of peptide bonds at LysArg—Xaa and ArgArg—Xaa to process yeast a-factor pheromone and killer toxin precursors. 

Zamir LO, Devor KA, Morin N, Sauriol F (1991) Biosynthesis of trichothecenes oxygenation steps post-trichodiene. J Chem Soc Chem Comm 1033-1034 McCormick SP, Taylor SL, Plattner RD, Beremand MN (1990) Bioconversion of possible T-2 toxin precursors by a mutant strain of Fusarium sporotrichioides NRRL 3299. Appl Environ Microbiol 56 702-706... 

Jimenez, E.C., B.M. Olivera, and L.J. Cruz Localization of Enzymes and Possible Toxin Precursors in Granules from Conus striatus Venom. Toxicon Suppl. 3, 199 (1983). 

Aeromonas hydrophila is a bacterium that causes diarrheal diseases and deep wound infections. These complications arise due to pore formation in sensitive cells by the protein toxin aerolysin. Proteolytic processing of the 52-kD precursor proaerolysin (Figure 10.34) produces the toxic form of the protein, aerolysin. Like a-hemolysin, aerolysin monomers associate to form a heptameric transmembrane pore. Michael Parker and coworkers have proposed... 

Since the unpurified toxins show no aldehyde absorption, it was of interest to identify the precursors of helminthosporol and helminthosporal. Thin-layer chromatography of fresh chloroform extracts of the toxin that had been concentrated below 40° indicated several spots (6). One was identified as prehelminthosporol, a hemiacetal (X), from NMR spectra and chemical reactions. Refluxing with triethylamine yielded helminthosporol, identical with Tamura s prod-... 

Similarly, when arrays of these test resonant cavities loaded with functionalized wicks for various toxins are phase-locked to the reference cavity as shown in Fig. 15.5 they can act as detectors for targeting various toxins as well as their precursors through an array of suitably tuned cavities with specifically functionalized nanotubes. By using the approach as demonstrated in this document, it has been shown that the apparatus can be used to successfully detect low levels of toxin vapors associated with the drag Methamphetamine, in a laboratory-controlled environment. Some of the results of this study are highly sensitive in nature and are not reported in this document. These results can be obtained by other avenues. 

Fig. 15.5 Arrays of cavities phase-locked to the reference cavity and loaded with functionalized wicks to specifically determine the toxin and its precursors...

In a limited number of NRPSs, the final module terminates in a specialized C domain that catalyzes chain release through amide bond formation. Modules of this type are found in the synthetases involved in the biosynthesis of enniatin, vibriobactin, cyclosporin/ HC-toxin/ and PF1032A. Unlike TE termination, this method of chain release does not utilize an acyl-ester intermediate. Most likely, the chain termination precursor is presented to the C domain as an aminoacyl-5-PCP substrate. Most of these specialized C domains... 

Muscarine is found in tiny amounts, usually under 20 pg/g, in other agaric genera, too, such as Amanita, Boletus, Hygrocybe, Lactarius, Mycena, and Russula. It was by the small amounts of muscarine present in A. muscaria, 90 pg/g, that the toxin was detected and identified (and got its name) but muscarine in A. muscaria usually does not account for the symptoms that occur after ingestion of this fungus, which are produced by muscimol and its precursor ibotenic acid. 

Transcription is catalyzed by DNA-dependent RNA polymerases. These act in a similar way to DNA polymerases (see p. 240), except that they incorporate ribonucleotides instead of deoxyribonucleotides into the newly synthesized strand also, they do not require a primer. Eukaryotic cells contain at least three different types of RNA polymerase. RNA polymerase I synthesizes an RNA with a sedimentation coef cient (see p. 200) of 45 S, which serves as precursor for three ribosomal RNAs. The products of RNA polymerase II are hnRNAs, from which mRNAs later develop, as well as precursors for snRNAs. Finally, RNA polymerase III transcribes genes that code for tRNAs, 5S rRNA, and certain snRNAs. These precursors give rise to functional RNA molecules by a process called RNA maturation (see p. 246). Polymerases II and III are inhibited by a-amanitin, a toxin in the Amanita phalloides mushroom. 

Prior to our understanding, there was only one reported experiment on the biosynthesis of PSP, in which C-amino acid precursors were fed to the culture of Gonyaulax catenella, and the incorporation of some radioactivity was observed in the crude toxin fraction (4). 

Scheme 4). This unexpected enrichment of two neighboring carbons from a single-labeled precursor can be explained by assuming that labeled glycine was introduced into TCA cycle via malate. In the cycle, the molecular asymmetricity will be lost at the succinate step, and the labeling will appear on both C-2 and C-3 of succinate. The result seems to support Scheme Ic, since C-4 and C-3 of glutamate correspond to C-11 and C-12 of the toxin molecule in such a scheme. 

Table I. Incorporation ratios of precursors into the toxins and gonyautoxin-III (GTX-III) produced by Gonyaulax tamarensis...

Feeding Precursors Amounts of toxins and isolated in mouse units (mu) radioactivity ... 

Precursor Amount of Crude Toxins Obtained Toxin isolated and amount Comments... 

The potential fate of an allelopathic chemical in the environment is outlined schematically in Figure 1. Donor plants produce toxins or their precursors, and these toxins are released into the environment. Whether there is "feedback control" or any other form of control over this process is unknown (28). 

A predominant toxin (51) from water beetles of the genus llybius (Table V) shows a UV absorption corresponding to hydroxyquinoline or hydroxyiso-quinoline. The H-NMR spectrum exhibits, beside signals of methyl ester and phenol, signals of five aromatic protons as both ABC and AB systems, the latter indicating two protons at C-3 and C-4 in quinoline. Since electron pyrolysis of 51 gives radioactive 8-hydroxyquinoline, its structure is identified as methyl 8-hydroxyquinoline-2-carboxylate (51) and confirmed by synthesis from xanthurenic acid (52) (Scheme 48) (101). The precursor of this alkaloid was shown to be tryptophan (444). 

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