Heat inactivation of bovine plasmin

• Published in: International dairy journal Vol. 8; no. 1; pp. 47 - 56
• Main Authors: Metwalli, Ali A.M, de Jongh, Harmen H.J, van Boekel, Martinus A.J.S
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 1998; Elsevier Science
• Subjects: Biological and medical sciences; denaturation; Food Chemistry and Microbiology; Food industries; Fundamental and applied biological sciences. Psychology; Geïntegreerde levensmiddelentechnologie en -fysica; heat inactivation; Integrated Food Science and Food Physics; kinetics; Levensmiddelenchemie en -microbiologie; milk; Milk and cheese industries. Ice creams; plasmin; VLAG; milk; denaturation; kinetics; heat inactivation; plasmin; Heat treatment; Serine endopeptidases; Enzyme; Temperature effect; Thermal denaturation; Inactivation; Mechanism; Plasmin; Thermal stability; Peptidases; Milk protein; Casein; Lactoglobulins; Disulfide bond; Hydrolases; Cow milk; Kinetic parameter
• ISSN: 0958-6946; 1879-0143
• DOI: 10.1016/S0958-6946(98)00017-X

The thermal behaviour of the protease plasmin was studied in the absence and presence of milk components. A global unfolding of the isolated plasmin occurred at 50–55°C, but secondary structure of plasmin increased with increasing temperature, possibly due to aggregation. Plasmin was reversibly inactivated between 55 and 65°C and was not subject to autoproteolysis. Irreversible inactivation (obeying first-order kinetics) started above 65°C with a temperature dependence typical for protein unfolding. Interaction with cystein caused irreversible (first-order) inactivation of plasmin from 45°C upwards; kinetics suggested a mixed mechanism of unfolding and SH/SS interaction. In agreement with literature, casein protected plasmin from irreversible inactivation while β-lactoglobulin increased inactivation. Casein partly compensated the destabilizing effect of β-lactoglobulin. The high heat stability of plasmin in milk products appeared not to be due to a high conformational stability, but to protection by casein towards irreversible inactivation of the unfolded enzyme.