The S2 fraction (ca 500 mg) was dissolved in 20 mL of 50 mM Tris HCl (pH 8.0) and transferred
into a dialysis tube (molecular weight cut-o®, 3500), then dialyzed against 1000 mL of 5.0%
acetic acid (AcOH) for 3 hr, and then 1000 mL of 5.0% AcOH for 8 hr.