DETERGENT TWEEN-80 MODIFIES THE SPECIFIC ACTIVITY OF PAI-1

In the measurement of the reaction between low concentrations of tissu e plasminogen activator OPA) and plasminogen activator inhibitor type- 1 (PAI-1) in buffer, a detergent is needed to optimize the assay and t o prevent unspecific adhesion. Not only the recovery, but also the act ivity of tPA and PAI-I depends on the type of detergent and its concen tration. Stable Values for the specific activities were obtained in th e concentration range of 0.03-0.3 g/L Tween. Moreover, it became appar ent that the composition of Tween also seems to affect PAI-1, since th e specific activity of PAI-1 in a buffer with Tween 80 from one source was approximately 40-50% lower than with Tween 80 from another source . SDS-PAGE confirmed the formation of a correspondingly smaller amount of stable complex with tPA, but also the concomitant appearance of cl eaved, 'substrate' PAI-1. The observed decrease in specific activity i n the reaction with tPA thus depends on an increase in the relative am ount of cleaved PAI-1. In contrast, the same high specific activity wa s consistently obtained with Tween 20 purchased from different sources . The difference between the different commercial preparations of Twee n 80 with regard to the properties of PAI-1 was also found in a clot l ysis assay in which thrombin, fibrinogen and plasminogen (the natural substrate for tPA) were used. Although we have not been able to identi fy a specific component in Tween, our observations can be of practical use for other workers in this field.