Substrates for kinin-releasing enzymes in human plasma.

Abstract

Abstract: Indirect evidence has been provided of the presence of 3 kininogen fractions: The average amounts of kinin released by human plasma kallikrein (1.2 μg/ml plasma) and by human urine kininogenase (2.4 μg/ml plasma) when added up exceeded the amount of kinin released by combined use of the two enzyme preparations (3.0 μg/ml plasma). Methods were as described by BRISEID et al. (1968). It is suggested that plasma kallikrein released kinin from 2 kininogen fractions, SI′ and SI″, and that urine kallikrein released kinin from 2 kininogen fractions, S1″ and S2. Repeated incubation with each of the kininogenase preparations did not increase the yield of kinin. Soybean trypsin inhibitor did not reduce the amount of kinin released by urine kallikrein. In control experiments a leucine aminopeptidase preparation transformed kallidin to bradykinin, but did not increase the kinin activity of the urine kallikrein incubates. Experiments carried out . with plasma kallikrein and padutin in 60°‐heated plasma supported the assumption of the 3 kininogen fractions.