Abstract
A complex of plasminogen activator inhibitor-1 (PAI-1) and PAI-1-binding protein (PAI-1-BP) contained S-protein (vitronectin), PAI-1 and unidentified 40-kDa protein on SDS-PAGE under reducing conditions. By Western-blot analysis, the 40-kDa protein was identified as SP-40, 40 using anti-SP-40, 40 antibody. Therefore, it was thought that PAI-1-BP consisted of S-protein and SP-40, 40. It is known that PAI-1 is a labile protein which becomes inactive during incubation at 37°C. However, after the incubation of PAI-1 with SP-40, 40 at 37°C for 1 h, PAI-1 could still form a complex with tissue plasminogen activator (tPA), and it inhibited plasmin formation in the mixture of plasminogen and urine plasminogen activator (uPA). The results clearly indicated that SP-40, 40 stabilized PAI-1 activity as well as S-protein did.
