S2251 plasminogen measurement - high values obtained even when enzyme absent? (Apr/26/2009 )

I have been doing the S2251 assay to measure plasminogen/plasmin in cell suspensions. To distinguish plasminogen from plasmin, some of the samples do not have the streptokinase enzyme added AND yet there are no differences when the enzyme is there/not for some of the samples. Has anyone had this before?

It's possible that your cells are secreting urokinase plasminogen activator (uPA), especially if they are phagocytic cells. This could stimulate your cells if there are any contaminating bacterial components in your streptokinase stock like LPS so you might want to assay it with media only to rule this out. I've had problems with this assay before too, but the experiment was very different. Hope this helps. Good luck!

-shawn