Studies on tissue thromboplastin. II. Species specificity.

Purified brain tissue thromboplastins of human, bovine and chicken origin have been tested on homologous and heterologous plasmas. Purified brain tissue thromboplastin is species specific. Lipid extracts from purified brain tissue thromboplastin prepared with pyridin show a negligable residual species specificity, probably caused by a slight contamination with brain tissue thromboplastin. The activity curves of our lipid extracts differ from typical curves expected for lipid activators by a less distinct inhibition in high concentrations probably caused by a different composition of petrol-ether and pyridin extracts. The protein part of tissue thromboplastin does not activate prothrombin in any system. The protein part of tissue thromboplastin of one species could be combined with the lipid part of another species to form an active tissue thromboplastin. The species specificity of these combinations was determined by the source of protein used.