Summary
Studies on antithrombin levels of heat-treated plasma showed that thrombin is rapidly
removed during the first five minutes of incubation and thereafter removed more slowly
until a plateau is reached at 25 minutes when about 20% of the thrombin remained regardless
of the initial amount.
The calcium requirements of thrombin activation were studied by using thrombin in
insoluble form bound to Sepharose - 4B. Calcium ions were not essential for activation
of factor XIII in plasma or purified factor XIII. With purified factor XIII calcium
ions decreased activation, whereas with plasma factor XIII calcium ions increased
activation.
Activation of plasma factor XIII can be accomplished by Reptilase or trypsin as well
as thrombin, when activity is measured by the ability to stabilise fibrin. When measured
by the dansyl cadaverine method, only Reptilase and thrombin activate factor XIII.
Arvin did not activate factor XIII and formed an unstable clot.
