Streptolysin O: sedimentation coefficient and molecular weight determinations.

The sedimentation coefficient of streptolysin O as determined by sucrose density gradient ultracentrifugation is 3.7S. An approximate molecular weight of 60,500 was calculated from the sedimentation velocity, and a similar value was obtained by Sephadex gel filtration. There was no measurable difference in the sedimentation coefficient of streptolysin O in either the active or reversibly inactive forms, indicating that there were at most only minor conformational differences between the two forms.