Characterization of select plasminogen activators from bovine milk and bacterial sources
Abstract
Plasminogen activators (PAs) are serine proteinases that convert plasminogen (PG) to plasmin (PL) in blood and milk. Due to large volumes of cheese produced in the U.S., large costs associated with ripening, and the important proteolytic role of PL in cheese production, PAs in milk and factors affecting their activation need to be fully understood. The overall objective of this project was to determine the effect of sample preparation and substrates on the PL enzyme system components in a cheese system and the characterization of PAs in milk, curd, and bacterial sources. The specific objectives were to determine: (1) the optimal sample preparation and substrate used in assays for PL, PG, and PAs in parts of the cheese system. (2) The major type of PA in milk and the effect of sample preparation and substrate in assays to measure bovine PAs. (3) The effect of incubation temperature and salt concentration on PAs in curd. (4) The potential PL enzyme system-like activity of Listeria monocytogenes . Plasmin enzyme system activities were determined using specific fluorometric and spectrophotometric substrates and specialized electrophoresis activity gels. The sample preparation and substrate type both had a significant effect on the measured PL system components, especially for PAs. The major type of PA in milk was tissue-type PA, and the Sup2 method isolated more of both PAs. Incubation temperature of curd significantly increased PL, PG, and uPA activity, but salt concentration only had a significant effect on PG. Both Escherichia coli O157:H7 and Listeria monocytogenes exhibited PL system-like activity. L. monocytogenes showed PA-like and PG-like activity that still needs to be confirmed for specificity. These findings suggest the possibility for accelerated ripening of cheese through tPA activation and that the PA-like and PG-like activity of L. monocytogenes could possibly contribute to the invasion/infection mechanisms of L. monocytogenes.
Degree
Ph.D.
Advisors
Hayes, Purdue University.
Subject Area
Food science
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