Purification of functional subunits of the eighth component of human complement (C8) under nondenaturing conditions

A simple procedure is described for purifying the noncovalently associated alpha-gamma and beta subunits of human C8 in the absence of denaturants and in yields significantly higher than previously obtainable. The procedure utilizes either conventional or high-pressure molecular sieve chromatography in the presence of 1.5 M NaCl. This ionic strength promotes dissociation of alpha-gamma from beta and facilitates their physical separation under mild conditions. Yields are typically 60-75% and, as judged by several criteria, each subunit is functionally identical to those isolated by earlier methods using sodium dodecyl sulfate. This new procedure eliminates the need for this detergent and thereby avoids the major solubility and yield problems encountered during its removal.