Heterodimer: presynaptic neurotoxin. Monomer: Snake venom phospholipase A2 (PLA2) is inactive towards micellar phosphatidylcholine but is weakly active towards non-micellar dithiolecithin. PLA2 catalyzes the calcium-dependent hydrolysis of the 2-acyl groups in 3-sn-phosphoglycerides. a 1,2-diacyl-sn-glycero-3-phosphocholine + H2O = a 1-acyl-sn-glycero-3-phosphocholine + a fatty acid + H(+) Binds 1 Ca(2+) ion. Heterodimer of an acidic subunit (CbIalpha or CbIbeta) and a basic subunit (CbII). The acidic subunit is non-toxic, and increases the toxicity of the basic subunit. Expressed by the venom gland. Belongs to the phospholipase A2 family. Group II subfamily. D49 sub-subfamily.