A collaborative study to establish a standard for high molecular weight urinary-type plasminogen activator (HMW/u-PA)

An international collaborative study involving eleven laboratories located in eight countries was undertaken to establish an International Standard for high molecular weight urinary-type plasminogen activator (HMW/u-PA). The current International Reference Preparation (IRP code numbered 66/46) for urinary-type plasminogen activator (u-PA) or urokinase (see Nomenclature footnote) is a 66/34 molar ratio mixture of low molecular weight (LMW)--and high molecular weight (HMW)--u-PA's and is considered unsuitable as a standard for homogeneous preparations of HMW/u-PA. The putative standard for HMW/u-PA (code number, 87/594) was compared for potency in a clot lysis assay with the current IRP for u-PA (code number, 66/46) and a lyophilised preparation of single chain urinary-type plasminogen activator (SCuPA), the latter being used in the assay without prior activation by plasmin to its active two chain form (TCuPA). Both the proposed standard for HMW/u-PA (87/594) and the SCuPA compared in a statistically satisfactory manner in parallel line bioassays with the current IRP for u-PA (66/46), thus allowing potency estimates to be obtained for these two materials in relation to defined international units. Data from the eleven laboratories indicated that each ampoule of the proposed standard for HMW/u-PA contained 4,300 i.u. of activity and was stable for over 1 year at 4 degrees C. Most participants indicated that SCuPA expressed only a small amount of its activity without a prior activator step and this suggests that SCuPA assays need to be preceded by a plasmin activation step.(ABSTRACT TRUNCATED AT 250 WORDS)