rd 23 Congress of the International Union for Biochemistry and Molecular Biology th 44 Annual Meeting of the Brazilian Society for Biochemistry and Molecular Biology th th Foz do Iguaçu, PR, Brazil, August 24 to 28 , 2015 PARTIAL CHARACTERIZATION OF AN EXTRACELLULAR PROTEASE OF Pseudomonas fluorescens Alves, M.P.1; Salgado, R.L.2; Eller, M.R.1; Carvalho, A.F.1 1 Departamento de Tecnologia de Alimentos da Universidade Federal de Viçosa, Minas Gerais, Brasil; 2Departamento de Bioquímica Agrícola da Universidade Federal de Viçosa, Minas Gerais, Brasil. Psychotropic bacteria play an important role in the deterioration of milk and dairy products since they produce heat-resistant proteolytic enzymes, which may remains active after heat treatments applied throughout their production. This study aimed the partial characterization of an extracellular protease produced by a proteolytic strain of P. fluorescens. The enzyme was partially purified from the supernatant of the culture of the bacteria P. fluorescens 07A by fractioned precipitation with ammonium sulfate, followed by size exclusion chromatography and concentrated using Amicon® Ultra-15. The effect of temperature and pH on protease activity was assessed using azocasein as substrate. The enzyme was incubated at temperatures ranging from 4 to 60 °C, and different buffers at pH values ranged from 4.0 to 10.0. By SDS-PAGE it was observed that the protease has a molecular mass of 50 kDa. It shows activity in a wide temperature range, 460 °C, with maximum activity at 37 °C. Moreover, more than 95% of the protease activity is maintained at 50 °C and above this temperature it is considerably reduced. The protease is also active over a wide pH range, from 5.0 to 10.0, with maximum activity at pH 7.5. Between pH 8.0 and 10.0 the protease activity remains constant, approximately 69% of the maximum activity. The wide pH and temperature ranges tested in this work in which the protease retains much of its activity include many of the storage conditions of milk and dairy products. The knowledge about the characteristics of proteolytic enzymes in order to control their production and activity in raw milk is essential to reduce the various technological problems caused by psychrotrophic bacteria in dairy products. Keywords: enzyme characterization, milk proteolysis, protease Acknowledges: CNPq, FAPEMIG, CAPES. Brazilian Society for Biochemistry and Molecular Biology (SBBq)