the eluting buffer and this peak corresponds to a small protein peak the fractions containing the highest activity are pooled to give 6 to 8 ml solution stored at 20 u00b0 c and which represents 70 to 80 of the activity applied to the column fractions containing low activity are pooled separately the total recovery of activity in both pools usually amounts to 90 to 100 the potassium thiocyanate eluate contains a single band of protein with a molecular weight of 72 000 daltons corresponding to a mixture of pure tpa and pro tpa the latter in different runs amounting to from 39 to about 50 of the total or more the yields improve if the same column is used repeatedly over and over again the column thus not only remains effective to be re used many times but in fact improves with use this is surprising because tpa has the property of cleaving the inhibitor de 3 when in its non immobilized form the pooled fraction containing tpa and or pro tpa are dialyzed against 0 30 molar sodium chloride containing 0 01 volume percent tween 80 prior to administration the concentration is adjusted to 75 u03bcg per ml of tpa plus pro tpa for therapeutic purposes the dosage rate for tpa is the same as for pro tpa and 0 3 molar nacl the solution is sterilized by filtration through an 0 22 u03bcm membrane filter.