The Natural Repertory of Prof. William Nelson

the victim so that the digestive system of the snake, which is not
extremely strong, can get a head start on the digestive process.
These venoms have strong pharmacological activity with a highly
specific mode of action. Most of the contents of these venoms are
proteins. Low molecular weight compounds such as peptides, nucleotides
and metal ion are also often present.
CLASSICS OF NEUROTOXINS
In the neurotoxin development there are two pharmacological classes
of neurotoxins: 1) those which are post-synaptic, and 2) those which are
pre-synaptic. Curare is an example of a post-synaptic neurotoxin. It
binds to the nicotinic acetylcholine receptors, and prevents the
depolarizing action of acetylcholine. These toxins are usually referred to
as curare-like toxins. Pre-synaptic toxins inhibit the release of
acetylcholine, and their toxicity is much higher than that of the post-
synaptic toxins.
Another type of toxin is the membrane toxins which change the
permeability of the membrane. They are often cardio-toxins, lytic factors,
cytotoxins, etc. These names indicate the types of membranes they affect.
Membrane toxins have been isolated only from elapid venoms. These
membrane toxins work by penetrating into the hydrophobic layer of the
membrane. Many of these toxins have phospholipase types of structures.
A secondary hypothesis is that the membrane might be disrupted by the
interaction of the disulfides in the toxin and the sulpha-hydro groups in
the membrane. These toxin-induced permeability changes can have
many biochemical and pharmacological activities. They might be
hemolytic which would allow for the disruption of red blood cells; or
cytotoxic, where they might induce a type of leukemia or lymphocytoma.
There is a depolarizing effect of the different membranes which can cause
peripheral nerve problems, contracture, paralysis, ventricular fibrillation
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