Heterodimer A-B: Nigroviriditoxin possesses phospholipase A2 (PLA2) activity. It consists of a non-covalent association of a basic PLA2 subunit B with a non-enzymatic subunit A. Subunit A: The acidic subunit of nigroviriditoxin probably is a heterotrimer of three disulfide-linked chains generated by post-translational maturation of a PLA2-like precursor (PubMed:20590130). It appears to have no PLA2 activity of its own, instead inhibiting the catalytic activity of subunit B (PubMed:25434534). It is not toxic to mice by itself but increases toxicity of subunit B (PubMed:25434534). Nigroviriditoxin is a heterodimer of an acidic subunit A and a basic subunit B. Expressed by the venom gland. Belongs to the phospholipase A2 family. Group II subfamily. D49 sub-subfamily. The order of the peptides is unknown.