Substances & Homeopatic Remedies

Theridion curassavicum

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Table 2. Toxic effect of various fractions of the Latrodectus venom (34-35)
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  Fraction           Frog        Mouse    Housefly         Crayfish          1964(33)         1972(34)
whole                   +        +           +              +
extract
  A                     -        -           -              -                                   A
  B                     +        +           -              -
  C                     +        +           +              -                LV1                C   
                                                                             LV2                B
  D                     -        -           -              -  
  E                     -        -           ND             +    
-------------------------------------------------------------------------
  B5                    +        +           -              -                LV3                D
  C3                    -        -           +              ND    
  C5                    +        +           +              ND    
  E2                    -        -           ND             +                LV4
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  Fractions A-E of Latrodectus venoms were referenced from work in 1976 (35).+, active; -, inactive;  ND, not
determined. LV1-LV4 were fractionated in 1964 (33). A-D were fractionated in 1972 (34).
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Study of LTX (alpha-latrotoxin): LTX interacts with lipid bilayers to make them permeable to certain ions and
appears more selective for alkali cations over anions. The bilayers definitely become permeable to Ca(II),
suggesting that permanent channels are formed in the lipid bilayer by LTX, and that these remain open (36). It
was also found that LTX prevented the uptake of labeled gamma aminobutyrate (GABA) and norepinephrine
by rat brain synaptosomes. The release of GABA that stimulated the LTX was not dependent on extracellular
Ca(II). The release of norepinephrine was Ca(II) dependent (37). The LTX stimulated the release of
transmitters, dopamine and norepinephrine in a neurosecretory cell line (PC12) derived from rat
phenochromocytoma in culture (38).
The amino acid composition of LTX, labeled LV3, was determined with a Beckman model 120 amino acid
analyzer and found to consist of 1219 residues; SDS polyacrylamide gel electrophoresis revealed its the
molecular weight to be 130 kDa (39). Variable results of the amino acid sequence of the LTX have been
reported by Russian workers (40). Thereafter, the total amino acid sequence of the LTX was deduced from
cDNA sequencing (41).The cDNA contained a 4203 base-pair open reading frame corresponding to the 156
855 Da protein composed of 1401 amino acids. Molecular weight differed from that earlier determined by
means of SDS gel electrophoresis. Therefore, the toxin can be considered as a precursor, and processing takes
place in the C-terminal region of the polypeptide chain during its maturation. This hypothesis seems more
reasonable because all studied peptides of tryptic hydrolysate are equally distributed in the toxin fragment with
coordinates 1-1170. Molecular mass of this fragment (Mr 131 kDa) is in good agreement with the apparent
molecular mass of the isolated toxin. Moreover, the C-terminal fragment of over 200 amino acid residues with
coordinates 1171-1381 was absent in the products of toxin tryptic hydrolysate despite many cleavable regions
(41). The highly purified toxin preparations were found to contain two components: polypeptides of 1401 (alpha
latrotoxin) and 70 (low molecular weight protein) amino acid residues (42).
The LTX is thought to act by binding to high-affinity receptors which are found in susceptible tissues (43,44).
This receptor is a member of the neurexin family of proteins (45) and is found in the membranes of presynaptic
nerve terminals where it interacts with synaptotagmin (a synaptic vesicle protein) (46). This neurexin-
synaptotagmin complex is thought to be important in neurotransmitter secretion (47,48). It has also been
suggested that neurexins are involved in cell recognition in the nervous system (49). The low molecular weight
protein named latrodectin contains 88 amino acid residues, but a fragment of 18 amino acid residues of the
protein is lost after protein maturation (50-52). This protein exhibits certain structural homology with
erabutoxin-a from the sea snake (42) and with the crustacean hyperglycemic hormones (53). Structural analogy
of two proteins is not necessarily associated with functional similarity. The function of latrodectin is not clear.  
Attempts have been made to identify the other black widow spider venom fractions which are responsible for
the effects observed on invertebrate tissues. A protein with a single band, alpha-latroinsectotoxin, was identified
as having a molecular weight of 120 kDa. Latroinsectotoxin has an amino acid content similar to that of LTX
and acts as a specific insectotoxin causing rapid transmitter release from insect nerve endings (54,55).