Y. Shimohigashi et al., LYSINE-49-PHOSPHOLIPASES A(2) FROM TRIMERESURUS-FLAVOVIRIDIS VENOM ARE MEMBRANE-ACTING ENZYMES, Journal of Biochemistry, 118(5), 1995, pp. 1037-1044
Basic proteins I and II (BP-I and BP-II) isolated from the venom of Tr
imeresurus flavoviridis (Habu snake) are isozymes of highly active Asp
-49-phospholipase A(2) (Asp-49-PLA(2)) and classified into the group L
ys-49-PLA(2). BP-II was found to elicit a strong contraction of guinea
pig ileum, and this activity was inhibited completely by 1 mu M indom
ethacin, an inhibitor of the arachidonate cascade. BP-II was inactive
in the Ca2+-free medium, and p-bromophenacylated His-48-BP-II was also
inactive, BP-II exhibited no binding affinity for the cells expressin
g PLA(2) receptors. These results indicated that the contraction elici
ted by BP-II is due to the hydrolytic action of BP-II, liberating arac
hidonic acid from the ileum phospholipid biomembranes, In spite of its
limited lipolytic activities (av. 0.9% of Asp-49-PLA(2)) against mono
mers and micelles of synthetic phospholipids, BP-II hydrolyzed conside
rably strongly the phospholipids in the artificial bilayer vesicles. A
rachidonic acid released from liposomes of idonoyl-gamma-stearoyl-L-al
pha-phosphatidylcholine was determined by HPLC, and the activity of BP
-II was estimated to be about 75% as compared to Asp-49-PLA(2). Liposo
mes encapsulating carboxyfluorescein exhibited a strong dye-leakage in
duced by BP-II in a concentration-dependent manner, only in the Ca2+-c
ontaining buffer. The net result from all these observations was that
BP-II, a Lys-49-PLA(2), is an enzyme that hydrolyzes the membrane phos
pholipids. In contrast to BP-II, BP-I was found to be considerably wea
k in hydrolyzing membrane phospholipids, although its activities were
distinct, BP-I and BP-II share a common sequence with the sole excepti
on of Asp-67 (BP-I) and Asn-67 (BP-II) in the aligned sequences, This
implies that the amino acid at position 67 of Lys-49-PLA(2)s is the re
sidue required for discriminatory recognition of beta-arachidonoyl-pho
spholipid membranes.