Caiman kininogen-like cysteine proteinase inhibitor

Kininogens are the major mammalian plasma cysteine proteinase inhibitors; a kininogen-like protein was also found in the snake Bothrops jararaca plasma. This communication describes a kininogen-like protein in plasma of Caiman crocodilus vacare. Caiman crude plasma, unlike snake plasma, contains a detectable cysteine proteinase inhibitor. The inhibitor was purified by DEAE-Sephadex ion-exchange chromatography and chromatography on carboxy-methylated-papain-Sepharose. The estimated molecular weight of Caiman cysteine proteinase inhibitor is 70,000. Caiman plasma also hydrolyzes plasma kallikrein synthetic substrates and inhibits trypsin. Reptilian kininogen may lack the site for interaction with plasma prokallikrein, and the sequence of the released kinin may be distinct from bradykinin. The poor effectiveness of bradykinin on reptile smooth muscle shows that the reptile kinin receptors may be adapted to a specific kinin.