PURIFICATION AND CHARACTERIZATION OF MULTISQUAMASE, THE PROTHROMBIN ACTIVATOR PRESENT IN ECHIS-MULTISQUAMATUS VENOM

The venom of Echis multisquamatus (Central Asian sand viper) contains a single prothrombin activator, designated multisquamase, which is str ucturally and functionally different from ecarin, the prothrombin acti vator from the venom of Echis carinatus (saw-scaled viper). Multisquam ase is comprised of a 58000 Mr and a 23000 Mr subunit that consists of two disulfide-linked chains of 12000 Mr and 10000 Mr, respectively. I n contrast to ecarin, which activates prothrombin and prethrombin 1 at comparable rates, and whose activity is hardly affected by Ca2+ or by changes in ionic strength, multisquamase hardly activates prethrombin 1; prothrombin activation requires Ca2+ and is strongly inhibited at high ionic strength. The most favourable kinetic parameters are observ ed at 1 mM Ca2+ and at low ionic strength (K-m = 0.085 mu M and k(cat) = 0.68 s(-1) at I congruent to 0.04). An increase in ionic strength c onsiderably reduces the rate of prothrombin activation, due to an incr ease of the K-m (K-m = 0.8 mu M and k(cat) = 1.03 s(-1) at I congruent to 0.2). Studies in plasmas from patients on oral anticoagulant thera py show that E. Multisquamatus venom only activates carboxylated proth rombin, whereas E. carinatus activates both prothrombin and descarboxy prothrombin. Thus, multisquamase-dependent prothrombin activation appe ars to require post-translational modification of the gla-domain. This venom prothrombin activator may, therefore, become a useful tool to q uantitate prothrombin and descarboxyprothrombin in cases where vitamin K-dependent carboxylation of prothrombin is impaired. (C) 1998 Elsevi er Science Ltd.