Kinin-converting activity in the dog pseudoglobulin fraction from heated plasma and kinin liberation from dog kininogen by guinea-pig coagulating gland kallikrein (CGK).

The pseudoglobulin fraction obtained from heated plasma (60°, 1 hr) of various animals (PFHP) is widely used as a substrate in kininogenase activity assay. In the present investigation, however, kinin-converting activity was found in dog PFHP ; namely 100 μg of synthetic kallidin was completely converted to bradykinin within 1 hr on incubation with 300 mg of dog PFHP. The converting activity could be destroyed by further heating at 100° for 30 min. Kinin-converting activity was present in various species of PFHP's, though the activity of dog PFHP was the most potent among the PFHPs checked in this investigation. The kinin liberated from dog kininogen by guinea-pig coagulating gland kallikrein (CGK) was also identified by chromatographic analysis and by the DNS method. It has been reported that CGK liberates bradykinin from dog kininogen but it is now clear that CGK in fact liberates kallidin, like other glandular kallikreins, and that the kallidin is further converted to bradykinin by the contaminating kinin-converting enzyme in the substrate preparation.