Abstract
We used the research quartz crystal microbalance (RQCM) to monitor regulatory effects of plasmin and trypsin in the presence of their inhibitor α(2)-antiplasmin. The gold surface of quartz crystals was modified with a β-casein layer that served as a substrate for protease digestion. The addition of plasmin or trypsin as well as their mixtures with α(2)-antiplasmin resulted in an increase of resonant frequency, f, and in a decrease of motional resistance, R(m), depending on the molar ratio of protease: antiplasmin. At equimolar concentrations of protease and α(2)-antiplasmin (5 nM:5 nM) full inhibition of protease activity took place. Monitoring of plasmin activity on an hourly and daily basis revealed a prominent effect of autolysis and decrease of plasmin activity in freshly activated samples. The degree of inhibition as well as plasmin half-life (t(1/2) = 2.48 ± 0.28 days) connected with its degradation was determined.