Separation of Two Different Substrates for Plasma Kinin-forming Enzymes

Abstract

THE formation and possible function of plasma kinins have attracted considerable interest during recent years. The kinins have been shown to be formed from a fraction within the α-2 globulins of the plasma by the action of several enzymes. Kinin-forming enzymes are present in several glandular secretions, such as saliva and sweat. Another type of enzyme, called plasma kallikrein, is present in an inactive form in plasma. The first two plasma kinins identified were bradykinin¹ and kallidin^2,3. Recently a third, methionyl-lysyl-bradykinin, has been prepared from bovine plasma⁴. It is not known, however, whether the various kinins are formed from one and the same substrate or if they originate from different substrate fractions within the α-2 globulins of the plasma. Nor is it known whether the various enzymes attack one and the same substrate molecule, or if they act on different ones.