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Hemorrhagic snake venom induces apoptosis in vascular endothelial cells. In a
previous report, we described the purification of a vascular apoptosis-inducing
protein (VAP) from Crotalus atrox [Masuda, S., Araki, S., Kaji, K. &
Hayashi, H. (1997) Biochem. Biophys. Res. Commun. 235, 59-63]. We report here
the identification of a second vascular apoptosis-inducing protein, VAP2, in
venom from C. atrox. When we fractionated crude venom from C. atrox by
isoelectric focusing, we found two proteins with apoptosis-inducing activity,
one was basic and the other acidic. The basic protein corresponded to VAP, and
we named the acidic protein VAP2. VAP2 was a monomeric protein with molecular
mass of 55 kDa and an isoelectric point of 4.5. VAP2 killed vascular endothelial
cells in culture, and the death of cells exhibited the characteristic features
of apoptotic activity of VAP2 seemed to be specific to endothelial cells, as
reported for VAP. The half-lethal doses of VAP and VAP2 were 0.3 microg/ml and
0.1 microg/ml, respectively. Analysis of the partial amino acid sequences of VAP
and VAP2 revealed similarities to members of the metalloprotease/disintegrin
family. The sensitivity of VAP2 to changes in pH and temperature was distinct
from that of VAP. Our results suggest that VAP and VAP2 are members of the
metalloprotease/disintegrin family.
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