Quantitative determination of Ca2+ effects on endotoxin removal and protein yield in a two-stage ultrafiltration process

Endotoxin subunits normally aggregate into vesicles with a molecular mass a round 1,000,000. Some proteins can bind and disaggregate endotoxin to form protein-endotoxin complexes, which makes endotoxin removal from protein sol ution more complicated. It is also known that divalent cations such as Ca2 can act as "bridges" between lipopolysaccharide subunits, causing large ve sicles to form. Such a property has potential utility in endotoxin removal from biological solutions. A two-stage ultrafiltration was used in this stu dy during which Ca2+ reaggregated lipopolysaccharide subunits in protein so lutions into large vesicles that hence were retained by a 300,000 nominal m olecular weight cutoff ultrafiltration membrane. After the reaggregation of lipopolysaccharide subunits, the endotoxin removal efficiency was in the r ange of 54.78 to 73.10%, meanwhile protein yield was in the range of 71.57 to 89.54% at various protein/endotoxin concentration ratios.