Effect of thermal treatment on the activation of bovine plasminogen

The effect of heat on plasminogen (PG) was studied in both buffer and milk. The denaturation temperature for bovine PG was determined. Kinetic analysis of heated PG was conducted using a coupled assay and Spectrozyme®PL. The effect of heat on PG activation was studied in milk samples with and without addition of PG activator. The temperature range for denaturation of PG was between 50.1 and 61.6 °C. The overall catalytic efficiency increased for PG heated to 60 °C and above, as indicated by the significant increase in kcat/KM. In a milk system, a significant increase in activation of PG was measured at 57 °C. A drop in activation of PG was observed at higher temperatures, suggesting counteracting effects of other milk components that were affected by heat. Results indicated that the increased activation of heated bovine PG observed in buffer and milk systems was probably due to the unfolding of PG as a result of thermal denaturation.