Comparative Studies on Heat Stability of Proteins of Thermophilic and Mesophilic Bacteria

1) The heat stability of the extractable proteins of bacterial cells was investigated, using cell-free extracts prepared from the lysozyme-treated celllysates as the test material. The results obtained with a thermophilic bacterium were compared with those obtained with mesophilic bacteria, including B. subtilis, B. megaterium, Sarcina lutea, and Micrococcus lysodeikticus.2) The thermophilic bacterial protein was found to be significantly more heat stable than the proteins of mesophilic bacteria such as B. subtilis, B. megateriuin, and Sarcina lutea, especially in the range of temperatures favorable for growth of the thermophil. Exceptionally high heat-stability was discovered in the case of Micrococcus lysodeikticus, more than two third of the protein in its original extract tolerating heat-treatment of 100°C for 10 minutes.3) The electrophoretic and ultracentrifugal patterns of the macromolecular constituents of the bacterial cells were investigated. The heatstability of each macromolecular component was investigated by detecting the corresponding changes in the electrophoretic and ultracentrifugal patterns of the bacterial extracts after heating at 65°C, 80°C and 100°C for 10 minutes. The results obtained with the thermophil were compared with those obtained with the mesophils.