Converts nitrite as the sole substrate to form nitric oxide gas (NO). NO(2-) serves both as an electron donor and as an electron acceptor. Binds to negatively charged cell surfaces of activated platelets; binds to L-a-phosphatidyl-L-serine (PS)-bearing phospholipid membranes. Once bound on an activated platelet, NP7 releases its stored nitric oxide gas (NO) into the victim's tissues while feeding, resulting in vasodilation and inhibition of platelet aggregation. Also acts as an anticoagulant by blocking coagulation-factor binding sites. Has antihistamine activity; binds histamine with high affinity. 2 H(+) + 3 nitrite = H2O + nitrate + 2 nitric oxide Binds 1 heme b (iron(II)-protoporphyrin IX) group per subunit. Optimum pH is 7.5. Expressed in the endothelial cells of the salivary glands. Belongs to the calycin superfamily. Nitrophorin family.