Biology Reference
In-Depth Information
marked differences are clearly related to size of the specimens studied. Further char-
acterization of this body size-yield volume relationship was reported by Chiszar
et al. (1992), who studied
B. irregularis
Duvernoy's secretion yields from several
weight classes of
B. irregularis
. Specimens
300 gm body weight produced 40 μL of
secretion with 2.3 mg solid, while those
900 gm yielded an average of 139 μL with
10.8 mg solids (Chiszar et al., 1992). Weight classes between these lower and upper
limits produced intermediate volumes. The yield volume statistically correlated with
the size classes of snakes (Chiszar et al., 1992). Similar findings were recorded by
Mackessy et al. (2006), who reported a varied yield according to size and an average
yield (collected with parasympathomimetic stimulation) of 500 μL with 19.2 mg sol-
ids (90% protein) from large specimens of
B. irregularis
.
Similarly, a further study of
B. irregularis
Duvernoy's secretion protein content
found that different size classes of
B. irregularis
produced Duvernoy's secretions
with protein content ranging between 66% and 100%, with smaller snakes having
higher protein content (Weinstein et al., 1993).
Studies of the lethal potency of secretion from
B. irregularis
similarly reflect differ-
ences related to body size, rather than ontogeny,
sensu stricto
(Weinstein and Kardong,
1994). Vest et al. (1991) reported an i.v. LD
50
of 80 mg/kg for secretion from smaller-
intermediate-sized specimens, while Weinstein et al. (1991) reported an i.p. LD
50
of
10.33 mg/kg for secretion from larger specimens (see Appendix B). This size-related
difference was further investigated by Weinstein et al. (1993), who reported i.p. LD
50
for
B. irregularis
secretion that ranged between 10.5 mg/kg (large snakes) to 34.13 mg/kg
(small snakes). The size-related differences in
B. irregularis
Duvernoy's secre-
tion yield, toxicity, and protein content are reflected in the secretion toxin content.
Weinstein et al. (1993) reported that acetylcholine receptor-binding (AchRB) activ-
ity of the secretion was higher in smaller snakes. Duvernoy's secretion from larger
snakes had little, if any, AchRB activity (Weinstein et al., 1993). These observations
were further expanded by Mackessy et al. (2006), who reported that an azocaseino-
lytic metalloprotease and acetylcholinesterase increased in activity with size/age of the
B. irregularis
specimens studied, while toxicity, highest in neonate snakes, decreased.
These investigators described prey specificity (saurian and avian) of the toxic activities
detected in these secretions (Mackessy et al., 2006). Secretions from either juveniles or
adults lack hemorrhagic activity (Vest et al., 1991; Weinstein et al., 1991).
Fast protein chromatographic fractionation of Duvernoy's secretion from large-
size
B. irregularis
resulted in two lethal fractions (Weinstein et al., 1991). The major
fraction contained three proteins with molecular masses 12.5-52 kDa and had an i.p.
murine LD
50
of 7.3 mg/kg. The second fraction exhibited proteolytic and myotoxic
activities and consisted of two proteins with molecular masses of 14.5-17 kDa. It had
an i.p. murine LD
50
of 3.7 mg/kg and caused myoglobinuria in mice injected with
lethal doses of the fraction (Weinstein et al., 1991).
Recently, a unique, heterodimeric, covalently linked three-finger-fold neurotoxin
(“irditoxin,” as noted earlier) from Duvernoy's secretion of
B. irregularis
was char-
acterized and structurally analyzed (Pawlak et al., 2009). This distinctive 17,112- Da
three-finger-postsynaptic neurotoxin exhibited specificity for birds and lizards and
was nontoxic to mice. This specificity was noted also in nerve-muscle preparations
