| Summary: | Several assays for plasminogen activator employ a direct assay method. These are remarkably sensitive methods, yet they suffer in comparison to the sensitivity of coupled methods. Coupling the assay with plasminogen not only amplifies the sensitivity by the multiplicative effect of plasmin, but insures that only those proteases specific for plasminogen are assayed. The choice of substrate for plasmin is critical. A thiol ester substrate, thiobenzyl benzyloxy-carbonyl-L-lysinate (Z-Lys-SBzl), has been synthesized which combines high k/sub cat/ with alkaline stability. In an effort to characterize the plasminogen activator from hepatoma tissue culture (HTC) and its hormonally-controlled inhibitor, Z-Lys-SBzl was used in a coupled approach providing an assay which is superior to the /sup 125/I-fibrinolytic assay. It is also extremely sensitive to plasminogen activator and can be used for routine analysis of purification as well as kinetic and binding studies. (ERB)
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