Two-dimensional SDS–polyacrylamide gel electrophoresis of heat-modifiable outer-membrane proteins

An examination has been made of the effect which temperature of solubilization has upon the subsequent migration in SDS–polyacrylamide gel electrophoresis of proteins from the cell envelopes of Escherichia coli K12 and Neisseria sicca ATCC 9913. Conventional electrophoresis in tubes revealed substantial differences in the staining patterns of gels, depending upon whether the envelope samples were solubilized at 37 °C or 100 °C; in the case of N. sicca at least 6 of 13 discernible bands displayed heat-modifiable behavior. The relationship of the bands produced by each of the two temperatures was investigated by a two-dimensional electrophoresis procedure, in which a sample was solubilized at 37 °C and run in a usual cylindrical gel; the entire gel was then resolubilized at 100 °C, and laid along an acrylamide slab for electrophoresis in the second dimension.It was found that "free endotoxin" of both organisms examined contained the same major proteins as the total envelope fraction, and that these free endotoxin proteins showed the same heat-modifiable properties as when present in total envelopes.