The Extractability of Inner-Membrane Proteins from Salmonella typhimurium Intact Cells, Spheroplasts and Inner-Membrane Fragments by Non-Denaturing Detergents

The effect of Triton X-100, Na cholate and Tween 80 on the solubilization of integral membrane proteins in intact cells, spheroplasts and inner-membrane fragments of Salmonella typhimurium was studied. The detergents were used in various concentrations (1.6 to 64 mM) and cytochromes b and d were used as marker to monitor the solubilization of membrane-bound proteins. Results showed that no inner-membrane protein solubilization was detected after the treatment of intact cells with detergents. The effect of Na cholate and Tween 80 on spheroplasts and inner-membrane fragments was also negligible in comparison to Triton X-100. Triton X-100 solubilized cytochromes from inner-membrane fragments more efficiently than from spheroplasts. The ratio of total protein solubilization to solubilize cytochromes showed that in spheroplasts this ratio was maximum at 1.6 mM Triton X-100 while it was maximum at 16-32 mM Triton X-100 in inner-membrane fragments. This difference between spheroplasts and inner-membrane fragments may be due to the orientation of the inner-membrane in spheroplasts (right side out) and inner-membrane fragments (in-side out as well as right side out), and to the presence of peripheral proteins attached to cytoplasmic membrane in spheroplasts.