摘要 : The thermal behaviour of plasmin was studied in the absence and presence of milk components (casein and whey protein). A global unfolding of plasmin occurred at 50-55deg C, but the secondary structure of plasmin increased with inc... 展开 The thermal behaviour of plasmin was studied in the absence and presence of milk components (casein and whey protein). A global unfolding of plasmin occurred at 50-55deg C, but the secondary structure of plasmin increased with increasing temperature, possibly due to aggregation. Plasmin was reversibly inactivated between 55 and 65deg C and was not subject to auto-proteolysis. Irreversible inactivation (obeying first-order kinetics) occurred at temperatures >65deg C with a temperature dependence typical forprotein unfolding. Interaction with cysteine caused irreversible (first-order) inactivation of plasmin at >=45deg C upwards. Kinetics suggested a mixed mechanism of unfolding and SH/SS interaction. In agreement with the literature, casein protected plasmin from irreversible inactivation while beta-lactoglobulin increased inactivation. Casein partly compensated for the destabilizing effect of beta-lactoglobulin. It is concluded that the high heat stability of plasmin in milk products is not due to a high conformational stability, but to protection by casein towards irreversible inactivation of the unfolded enzyme. 收起