Scorpion® probes

Several proprietary fluorescence dye-based detection systems that characterize and quantify probe-bound nucleotide sequences have been developed and commercialized in recent years. For example, general and nonspecific DNA dyes can be used that bind with any double-stranded DNA (i.e., the probe-strand complex or otherwise) and are useful in gel electrophoresis. Much more sophisticated systems rely on oligonucleotide probes that incorporate fluorescent dyes that illuminate when a match between complementary strands are made. Included among the latter are TaqMan , molecular beacons, and Scorpion probes. 

Figure 16.7. Schematic representation of Scorpion probe reaction with target DNA sequence. Copyright 2005 and adapted with the kind permission of Invitrogen Corporation.

The three main categories of hybridization probes for real-time PCR are (1) cleavage based assays such as TaqMan, (2) displaceable probe assays such as Molecular Beacons and (3) probes which are incorporated directly into primers such as Scorpions. 

More recently double stranded DNA-binding dyes, (e.g., SYBR Green), have been introduced (Giulietti et al. 2001) which removed the need for an expensive, specific probe to be designed. Other sophisticated tools have been developed to work in conjunction with the Taqman method, for example molecular beacons, scorpions and hybridisation probes. These techniques rely on the FRET (Fluorescence Resonance Energy Transfer) principle but do not require the nuclease activity of the Taq polymerase. The different real-time... 

Finally, late in 1999, Delepierre et al.204 reported a comprehensive H-NMR analysis of the Pi7 peptide from the scorpion Panadinus imperator, again using Nano-probe technology to facilitate the acquisition of data with the small samples available. 

Only two reported applications of Nano-probe technology appeared in 2002. The first was a report detailing the solution of the 3D structure of small scorpion toxins present in nano-molar amounts in venom by Delepierre.216 The other report by Wang et a I.2 1 reviewed the application combined application of LC-NMR and Nano-probe technologies for the analysis of mixtures of natural products. 

III) Allele specific hybridisation (Figure 2) Fragments amplified in an allele unspecific PCR are measured with allele specific probes (Molecular Beacons, TaqMan probes or Scorpion), which can either be used in a single PCR or in multiplex reactions for detection of both alleles in one reaction [13]. This method has minor background problems, however the dynamic range may be limited due to competition of the probes. The Molecular Beacon proach has been developed for B. graminis and M. fijiensis [13]. 

Fluorescence Resonance Energy Transfer Fluorescence resonance energy transfer (FRET) real-time PGR method depends on the introduction of fluorogenic-labeled probes affected by the 5 nuclease activity of Taq DNA polymerase. The FRET method includes the TaqMan , molecular beacons scorpions and few other techniques, all of them are hybridization probes relying on fluorescence resonance energy transfer (FRET) to quantify PGR product via the generation of a fluorescent signal. 

Calcium ions are critical in the release of neurotransmitter substances at chemical synapses, and intracellular buffering mechanisms, possibly through a Na/K—ATPase mediated exchange [22], are important in controlling the release of Ca " ions and thus release of the neurotransmitter. The blocking of calcium transport by ruthenium red increases the spontaneous release of neurotransmitter [23]. The utility of these effects as probes is shown by the fact that acetylcholine release induced by tityustoxin, a scorpion neurotoxin, was shown to be enhanced by ruthenium red the stimulation was Ca-dependent and thus the conclusion was reached that free calcium, caused by competitive binding of ruthenium red to receptors, increased the release of acetylcholine [24]. 

Arthropod-derived toxins are also among the list of classical examples of toxins used to probe biochemical processes. Scorpion toxins have been important in the experimental determination of the spacial arrangement of residues on the potassium channel (11), and also in the inference of properties of its quaternary structure (12). A scorpion toxin was used as a tool in the first isolation of a specific component of an insect sodium channel (13). Spider toxins have been similarly useful in characterization of calcium channels (14). 

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