The species specificity of thromboplastin (tissue factor) is an important fact to take into consideration when clotting assays or experiments are planned. We have (re)investigated all possible combinations of thromboplastin and plasma from several of the most commonly used species of experimental animals.

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An immunoradiometric assay for tissue thromboplastin has been established. Blood levels in 6 patients undergoing total hip replacement have been determined. In 3 patients, high levels of circulating apoprotein III were found at various stages of the operation, showing a release of tissue thromboplastin chiefly during impaction of the prosthesis into the femoral bone. The other 3 patients had low or undetectable levels.

SummaryThe activation of factor IX purified from human plasma has been studied. Factor XIa and kallikrein separately activated factor IX to factor IXa. In both cases factor IX a had an apparent molecular weight of about 42–45000 in sodium dodecyl sul-phate-polyacrylamide disc gel electrophoresis compared with a molecular weight of about 70000 for the native factor IX. The activation by XIa required Ca2+-ions whereas Ca2+-ions did not influence the activation by kallikrein. A mixture of tissue thromboplastin and factor VII or RusselPs-viper venom alone did not activate factor IX. Trypsin activated and plasmin inactivated factor IX.

SummaryAntithrombin III, purified to homogeneity according to Polyacrylamide gel disc electrophoresis and immunoelectrophoresis, inhibited the activity of purified factor IXa and Xa, whereas factor VII was not inhibited either in the active or in the native form.Antithrombin III is the single most important inhibitor of factor Xa in plasma. Factor Xa does not, however, reduce the activity of antithrombin III against thrombin.

Summary1. Sodium deoxycholate (DOC) splits tissue thromboplastin into two inactive parts, fraction A and fraction B, separable by gel filtration in the presence of DOC.2. By recombination and subsequent removal of the DOC, the fractions reaggregate and regain full thromboplastic activity.3. Fraction A consists mainly of protein, while phospholipid is the main constituent of fraction B.

SummaryMonospecific antisera against the purified protein component of tissue thromboplastin (apoprotein-III) from human brain have been raised in goats and rabbits. The antisera neutralized tissue thromboplastin prepared from brain, thyroid gland and pulmonary tissue, indicating that apoproteins in the various preparations cross-reacted immunologically and therefore were similar or identical.Comparison of the activities of tissue thromboplastin preparations from 34 different areas of the brain demonstrated a characteristic distribution pattern and a wide range of activities. White and grey matter from the same areas had similar activities. Bulbus and tractus olfac-torius, medulla oblongata, corpus pineale, hippocampus and hypothalamus contained 160–270 % of the average activity, whereas cerebellum, globus pallidus, nucleus ruber and substantia nigra contained 30–60 %. The distinct distribution pattern was unrelated to tissue vascularization, and may suggest that apoprotein-III could serve other functions, apart from the coagulation of blood. The predominance in phylogenetically older brain regions would suggest that it represents a primitive or fundamental feature.

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