A new vasopeptide formed by the action of a Murphy-Sturm lymphosarcoma acid protease on rat plasma kininogen.

A new vasoactive peptide, formed by the action of a Murphy-Sturm lymphosarcoma acid protease on rat plasma kininogen was purified by gel filtration on Sephadex G-50 (fine) and fractions assayed on the isolated rat uterus for smooth muscle stimulating activity. The most active fraction was purified further by CM-cellulose chromatography. High voltage electrophoresis showed the peptide to be one component (Mgly 2.49) with an electrophoretic mobility different from bradykinin, lysyl-bradykinin and methionyl-lysyl-bradykinin. The molecular weight of the peptide was estimated on Sephadex G-25 column to be 1460. The amino acid composition was determined and the carboxyl terminal sequence identified by carboxypeptidase Y treatment to be Pro-Phe-Arg-Leu. Dansyl-Edman procedure yielded an amino terminal sequence of Ile-Ser-Arg-Pro. The peptide produced a dose-dependent contraction of the isolated guinea pig anterior mesenteric vein and relaxed the rabbit superior mesenteric artery contracted by phenylephrine.