Some components of the kinin system in Cohn's unheated human plasma proteins.

The presence of a kininase and a kininogenase was demonstrated in unheated human plasma proteins. The kininase was found to inactivate synthetic bradykinin and a kinin-like substance released from a kininogen-like material in unheated plasma proteins by human urinary kallikrein. It was heat-labile and inhibited by EDTA, HgCl2 and 1,10-phenanthroline. This enzyme was estimated to be kininase I from its inhibition pattern. Inactivation of the kininase revealed the presence of a kininogenase. Five per cent heat-treated human plasma protein solution has been demonstrated to have no kininase activity but to contain the kinin-like substance. A mechanism for the formation of the kinin-like substance in 5 per cent heat-treated plasma protein solution was discussed in terms of these kinin forming components present in the unheated plasma proteins.