Stabilities of UK, Pro-UK and UK-UK inhibitor complex in human plasma

Recently, we reported that fibrin high-affinity urokinase (Fib-UK) of which molecular weight was about 100K was present in human urine and was very similar to UK-UK inhibitor complex in immunological and enzymatic nature (3). In the present paper, stabilities of UK, pro-UK and UK-UK inhibitor complex in plasma were examined with zymography. UK-UK inhibitor complex which was formed by incubating UK and plasma was more stable in plasma than UK, and resistant to DFP. Similarly, pro-UK was most stable in plasma and resistant to DFP. These results suggest that when UK is bound to UK inhibitor, UK changes its comformation and its stability in plasma increases like pro-UK.