Snake venom phospholipase A2 homolog that lacks enzymatic activity. Is myotoxic and induces a dose-dependent edema in the mouse foot pad (PubMed:2781572, PubMed:9839670). Also exhibits strong anticoagulant effects by binding to factor Xa (F10) and inhibiting the prothrombinase activity (IC(50) is 3 nM) (PubMed:18062812). In addition, it shows cytotoxic activity to a variety of cell types and bactericidal activity to a variety of Gram-negative and Gram-positive bacteria (PubMed:7886694, PubMed:9654096, PubMed:9920486). Also induces a very rapid release of large amounts of potassium ions and ATP from muscle cells, which accounts for the pain reaction characteristic of viperid envenomations (PubMed:20660736). The released ATP amplifies the effect of the myotoxins, acting as a 'danger signal', which spreads and causes further damage by acting on purinergic receptors (PubMed:20660736). A model of myotoxic mechanism has been proposed: an apo Lys49-PLA2 is activated by the entrance of a hydrophobic molecule (e.g. fatty acid) at the hydrophobic channel of the protein leading to a reorientation of a monomer (By similarity). This reorientation causes a transition between 'inactive' to 'active' states, causing alignment of C-terminal and membrane-docking sites (MDoS) side-by-side and putting the membrane-disruption sites (MDiS) in the same plane, exposed to solvent and in a symmetric position for both monomers (By similarity). The MDoS region stabilizes the toxin on membrane by the interaction of charged residues with phospholipid head groups (By similarity). Subsequently, the MDiS region destabilizes the membrane with penetration of hydrophobic residues (By similarity). This insertion causes a disorganization of the membrane, allowing an uncontrolled influx of ions (i.e. calcium and sodium), and eventually triggering irreversible intracellular alterations and cell death (By similarity). Heparin inhibits the myotoxic activity (PubMed:7961981). Suramin inhibits the myotoxic activity (PubMed:15961104). High level of membrane cholesterol content reduces cytolytic activity, whereas low level of membrane cholesterol content increases cytolytic activity (PubMed:21506137). Cytolytic activity upon C2C12 cells is completely abolished at 15 degrees Celsius or below. Homodimer; non-covalently linked (PubMed:1899180, PubMed:2781572, PubMed:7718570, PubMed:15299297). Binds to heparin (PubMed:7961981). Expressed by the venom gland. It binds long-chain fatty acids covalently by a rapid, spontaneous, and autocatalytic process. When acylated, it binds to the surface of liposomes and isolated muscle membranes, with the fatty acid moiety inserted into the lipid bilayer and possibly acting as an anchor (PubMed:7718570). snakes from Pacific region, Monoisotopic mass. snakes from Caribbean region, Monoisotopic mass. K49-P1-20, a twenty-residue N-terminal peptide that corresponds to residues 17-36 of myotoxin II, enhances the activity of endothelin converting enzyme-1 (ECE1) and neprilysin (MME), two enzymes that degrade amyloid beta in the brain. It could be an excellent research tool to study mechanisms of ECE1 and MME stimulation, and a potential novel drug lead in the fight against Alzheimer's disease. Belongs to the phospholipase A2 family. Group II subfamily. K49 sub-subfamily. Does not bind calcium as one of the calcium-binding sites is lost (Asp->Lys in position 64, which corresponds to 'Lys-49' in the current nomenclature).