Activation of Factor XII in Rat Plasma: Protection by Benzamidine of the Cofactor Function of High Molecular Weight Kininogen

Abstract

Factor XII has been assayed as kaolin‐activated prekallikrein activator in rat citrated plasma pretreated with acetone (Briseid et al. 1978 & 1979; Briseid & Berstad 1979). In the present work benzamidine added during blood collection increased the extent of activation by a factor of 6. Rat high molecular weight kininogen (HMWK) added to acetone‐treated citrated plasma likewise increased the activation, providing evidence of the protection by benzamidine of the cofactor function of HMWK. All cofactor capacity was retained after the removal of the kinin part of HMWK. Experiments carried out with plasminogen‐free plasma showed that plasmin could hardly be the factor responsible for the destruction of HMWK. The stoichiometric factor XII concentration‐effect curve obtained by diluting acetone‐treated rat plasma with acetone‐treated human factor XII deficient plasma showed that factor XII is present in functional excess, the concentration of HMWK deciding the extent of activation. By diluting acetone‐treated rat plasma with buffer, HM WK concentration‐effect curves were obtained which were approximately linear over a range of 0.03–0.40 μg (bradykinin equivalents) per ml kaolin incubate. No further activation of factor XII was obtained at 0.80 μg/ml.

Activation of Factor XII in Human Plasma: Protection by Benzamidine of the Cofactor Function of High Molecular Weight Kininogen

“…In accordance with the above-mentioned statements in relevant literature on the stability of the kinin-free protein against further destruction by plasma kallikrein, we found no loss of cofactor capacity when purified human HM,K was incubated with purified human plasma kallikrein before being tested in cofactor assays (table 4). The results accordingly seem to indicate the presence in acetone-treated human plasma of a serine-protease capable of lowering the cofactor function of kinin-free HM,K, as has previously been registered in rat plasma (Briseid & Berstad 1981;Berstad & Briseid 1982;Briseid & Briseid 1983).…”

“…2. The decreased extent of activation of factor XI1 registered for the highest HM,K concentration used (table 2, 0.26 pg HM,K as bradykinin equivalents per ml kaolin incubate) has previously been registered also in rat plasma (Briseid & Berstad 1981). In experiments with purified factors from human plasma Meier et al (1977) also registered an inhibitory effect of HM,K on the PKA-activity generated when high concentrations of HM,K were used.…”

“…1976), that of human HM,K is fully retained in the kinin-free protein (Thompson et al 1978;Kerbiriou & Griffin 1979;Schiffman et al 1980;Mori & Nagasawa 1981). Studies of rat plasma, however, indicated that a plasminogen activator might be responsible for the loss of cofactor capacity of HM,K in rat plasma in the absence of benzamidine (Briseid & Berstad 1981;Berstad & Briseid 1982). This activator has been partially purified (Johansen & Briseid 1983) and was found to cause an extensive lowering of the functional activity of human HM,K too (unpublished experiments).…”

Reduced Cofactor Function of Human High Molecular Weight Kininogen Induced by Rat Plasma Kallikrein

“…In the crude plasma preparation used as a source of factor XII, HMrK is protected from destruction by an acetone-activated serine protease by the presence of benzamidine (7.5 mM). During the kaolin treatment of the diluted plasma a partial destruction of the HMrK cofactor activity takes place, reducing the extent of activation of factor XI1 correspondingly (Briseid & Berstad 1981;. Purified HMrK added before the activation with kaolin stoichiometrically increased the yield of factor XIIa ( fig.…”

“…Preparations of human plasma kallikrein significantly reduced the capacity of human high molecular weight kininogen (HMrK) to function as a cofactor in the surfacemediated activation of factor XI1 in a crude plasma preparation (Johansen & Briseid 1984a & b). Indirect evidence had been provided previously that the cofactor capacity of HMrK in rat plasma could be strongly reduced by the effect of an acetone-activated serine protease possessing plasminogen activator (PGA) activity (Briseid & Berstad 1981;Berstad & Briseid 1982). Later reported on the separation of rat plasma kallikrein into fractions with different PGA activities.…”