Protein separation using non-ionic and cationic surfactant precipitation

BACKGROUND

The predominant use of anionic surfactants to precipitate high isoelectric point (pI) proteins has increased in recent years, simplifying downstream separations. However, few researchers have tested cationic and non-ionic surfactants, whose properties are more desirable. This paper examines the effect of these surfactants on the precipitation efficiency of lysozyme, trypsin inhibitor and bovine serum albumin (BSA).

RESULTS

Precipitation of BSA and trypsin inhibitor using the cationics, trioctylmethylammonium chloride (TOMAC) and dimethyl dioctadecyl ammonium chloride (DODMAC) was evaluated, with TOMAC being superior. More than 90% of BSA was precipitated using TOMAC at pH 9.0 with a molar ratio of surfactant/protein (R) of 100:1, while 88% was precipitated using DODMAC. However, for trypsin inhibitor, only 58% was precipitated at an R of 61:1 and pH 6.2 using TOMAC. Protein precipitate recovery using the anionic surfactant sodium bis-[2-ethylhexyl] sulfosuccinate (AOT) was effective only with trypsin inhibitor, with 100% of the protein being recovered.

CONCLUSIONS

This study shows the potential of cationics to precipitate low pI proteins, and recover them using the counterionic surfactant AOT, with 100% recovery of trypsin inhibitor. However, non-ionic surfactants were ineffective. The method not only separates, but also preserves protein structure; hence cationic surfactants for low pI protein separation are promising.