Blood-sucking insects have bio-active substances in the salivary glands. These substances have activities on host blood coagulation system, hemostasis and blood vessel. Recently many of those molecules were isolated and characterized, and some of their genes have been cloned. We extracted and purified multiple hemoproteins from the salivary glands of reduviid bug, Rhodnius prolixus, and the cDNA of these proteins were cloned. We clarified that one of these proteins with a molecular weight of approximately 20,000 (designated as Prolixin-S) is not only an anticoagulant that inhibits an intrinsic coagulation factor (IX/IXa), but also a relaxant of vascular smooth muscle. We found that Prolixin-S binds with the smooth muscle relaxant nitric oxide NO that is synthesized in the salivary glands, and is injected into host during blood sucking, then release NO and relaxes the host blood vessel. That is, Prolixin-S reversibly binds with NO and function as a NO carrier.
