[[alternative]]Characterization of extracellular protease from the isolation Serratia plymuthica

[[abstract]]Serratia plymuthica, a psychrotropic bacterium isolated from a refrigerating environment was found to produce an extracellular protease functioning on a wide range of temperature from a low 4℃ to a moderate 37℃. Crude extracts of this enzyme was characterized regarding to its properties, its production and regulation of its enzyme activity. Particularly, effects on the growth of Serratia plymuthica and its extracellular protease production by varying amino acid end-products were extensively investigated. Physically, a proteolytic enzyme activity separated on a sodium dodecyl sulfate-gelatin-polyacrylamide gel electrophoresis was located on a spot corresponding to 48 kDa. Addition of L-valine, L-cystein monochloride and L-threonine as the carbon and energy sources to a mineral medium, exhibited an inhibitory effect on the growth of this bacterium. On the contrary, addition of DL-alanine, L-serine and L-glutamic acid as the carbon and energy sources to a mineral medium, an accelerating promotion of growth was observed. Whereas, using (NH4)2SO4 as a replaced nitrogen source in the same basal medium for culturing, no any effects were appeared. Regulatory effects by various amino acids on the synthesis of extracellular protease by Serratia plymuthica were also evaluated. Its proteolytic activity accumulated in the growth medium was feedback inhibited by many different amino acids including L-serine, L-glutamic acid, or L-cystein monochloride and (NH4)2SO4 plus 1% gelatin as a protein source. However, the most striking characteristic pattern of changing protease yields was exhibited by using DL-alanine as an interesting regulator. When increasing concentrations of DL-alanine (0 to 0.25%) were added to the culture media, yields of protease were also gradually increased until reaching a maximum level corresponding to 0.25% of DL-alanine. Beyond that, any concentrations of DL-alanine present in the medium exceeding 0.25% resulted in lowering yields of this extracellular enzyme. Apparently, Serratia plymuthica has evolved a very simple regulatory mechanism by using alanine both as a protease inducer and an inhibitor. When this bacterium senses a lower concentration of alanine in environment, it responses by producing more protease in order to harvest more amino acids substrates; otherwise, stops protease production.