Plasminogen activator from cultured baby hamster kidney cells

A large number of cell clones were isolated which produced different amount of extracellular plasminogen activator. These clones were identified and selected by use of an overlay medium containing casein and plasminogen. All cells obtained by this method arose from a high passage cell line (BHK-21/N) which had been originally cloned from BKH-21/C13 cells. These cloned isolated from BHK-21/N were characterized with respect to their growth rates and efficiencies of plating in soft agar and on plastic surfaces. No correlations were found between any of these growth properties and the amounts of extracellular plasminogen activator as detected in serum-free cell culture media. A plasminogen activator which was produced by a high passage hamster kidney cell (Hpa-6) was characterized biochemically. The enzyme was found to be inhibited by diisopropylfluorophosphate and therefore was considered serine protease. Hpa-6 antivator was also found to react with plasminogen in a manner which was indistinguishable from the action of urokinase on the proenzyme. Evidence was obtained which suggests that the activator can hydrolyze either of the two molecular forms of plasminogen, i.e., plasminogen with glutamic acid amino terminus or plasminogen with lysine amino terminus at a single position to yield active plasmin. The cellular localization of the Hpa-6 cell plasminogen activator was examined and the results obtained indicate that this activity was largely associated with the plasma membrane.