[Qualitative and quantitative determinations of staphylokinase-activity (author's transl)]

Staphylokinase (SAK)-activated plasminogen reacted specifically with nitroanilide (N-benzoyl-DL-lysine-4-nitroanilide) to form intensively yellow 4-nitroaniline. This reaction did not occur with staphylococcal proteases. For qualitative SAK-determinations nitroanilide was incorporated in an agar medium. SAK diffused into the medium and caused a distinct change in color from white to yellow. For quantitative SAK-determination the conversion of colorless nitroanilide to yellow 4-nitroaniline was recorded photometrically at 405 nm. The optical density correlated well with SAK-activity of preparations with different degrees of purity (fig. 1, 2). Another quantitative procedure for SAK-activity could be conducted with fibrin in microtiter-plates (Fib-MTT). In this method, after 2-fold dilutions of SAK-preparations fibrinogen (stained blue with astrazonblue) and subsequently thrombin were added. SAK-activity was indicated by lysis of the blue-colored fibrin clots in the microtiter-plates (fig. 3). The Fib-MTT was particularly suitable for measuring wide ranges of SAK-activities.