The mechanism of a one form model of prothrombinase for the activation of prothrombin proposed by NG [8]. The mechanism for the activation of prothrombin to thrombin by prothrombinase is achieved through two distinct intermediate pathways. In the scheme, a dotted arrow represents a channeling process and a thick arrow represents a ratcheting process (as defined by Ref.8). The notations for the scheme are as follows: E: enzyme (prothrombinase), P: prothrombin, M: meizothrombin, P2: prethrombin-2, M1: ratcheted meizothrombin, P21: ratcheted prethrombin-2, T: thrombin, •: complex form, (E•P)1 and (E•P)2: enzyme-substrate binding complex forms of prothrombin and prothrombinase, k with subscripts: kinetic constants for forward elementary reactions, and j with subscripts: kinetic constants for reverse elementary reactions.