PROBLEM TO BE SOLVED: To obtain the subject new protein, No-r protein S, exhibiting vasohypotonic activity, blood platelet agglutination inhibitory activity and phylactic activity, and useful as e.g. a vasohypotonic agent, by binding nitrogen monoxide to a protein isolated from the salivary gland of a sucking insect.
SOLUTION: This protein is new NO-r protein S which is formed by binding nitrogen monoxide (NO) to r-protein S, a protein isolated from the salivary gland of sucking insects, produced by cloning and composed of a base sequence- amino acid sequence of the formula. This new protein has vasohypotonic activity, blood platelet agglutination inhibitory activity and (bio)phylactic activity, being useful, as a vasohypotonic agent, for treating/preventing hypertension, lung hypertension, myocardial infarction, cerebral infarction, pulmonary infarction, vasospasm following subaracthnoid hemorrhage, etc. This protein is obtained by the following process: the salivary gland of a sucking insect (e.g. Rhodnius prolixus) is withdrawn, frozen with e.g. liquid nitrogen and ground in a physiological saline solution, and the resultant liquid is centrifuged, the resulting supernatant is fractionated by chromatography and the resulting active fraction is taken, and an NO gas-saturated liquid is then added to the fraction.