Asp49 plays a key role coordinating calcium in the catalytic site of phospholipases A 2 (PLA 2 ’s), thus assisting the stabilization of the ES intermediary transition state, which induces the enzyme activation. In this work, molecular dynamics simulations of an acidic PLA 2 from the venom of Agkistrodon halys pallas were performed in water, methanol and octanol. Because of the low affinity of svPLA 2 ’s for calcium ion in aqueous systems, different positional restraint forces were applied and the coordinates describing svPLA 2 –Ca 2+ ligand properties were simulated and evaluated. The results of the simulations were used to propose an interfacial activation model for svPLA 2 ’s. In this model, events related with enzyme activation involve: (a) the reorganization of calcium binding loop at membrane proximity followed by the Ca 2+ uptake; (b) side chain reorientation of Trp31, which defines a new specificity pocket for the phospholipid chain; (c) reduction of the distance between His48 and Asp49, increasing the nucleophilicity of Nε−His48; (d) side chain reorientation of Lys69 concomitant with projection of the 69-loop to solvent. In addition to existing biochemical and crystallographic data, our results allow us to describe a more detailed model for the interfacial activation of phospholipases A 2 .