Abstract
In the present paper we have characterized the plasminogen activators (PA) synthesized by 25 different human cell lines. Technically easy methods were adopted for concentration and immunological characterization of the activators even in the presence of PA inhibitors. Most cell lines produced uโPA (mol. wt 55,000), melanoma and HeLa cells tโPA (mol. wt 66,000) and two carcinoma cell lines and normal skin fibroblasts produced no detectable PA. The classical ^125^Iโfibrin method was compared to a caseinolytic assay and some of the discrepancies between results obtained with the two methods were shown to be due to cellโderived NaDodSO~4~โsensitive proteinase inhibitors in culture media. Additionally, synthesis and uptake by the cells of the wideโspectrum proteinase inhibitor alphaโ2โmacroglobulin (alpha~2~M) were studied by radioimmunoassay and immunofluorescence. No production of alpha~2~M could be measured in any of the malignant cell lines. In normal cells no correlation existed between the production of alpha~2~M and the observed inhibition of PA activity, which indicates that other proteinase inhibitors are produced by the cells.