Effect of cationic polymer adsorbent pK(a) on the selective removal of endotoxin from an albumin solution

To obtain fundamental information about the surface-environment effect of a dsorbent on the selective adsorption of endotoxin (lipopolysaccharide; LPS) from a protein solution, crosslinked poly(epsilon -lysine) (PL) and aminat ed poly(gamma -methyl L-glutamate) (PMLG-NH2) spherical adsorbents were pre pared. The apparent pK(a) (PKa,app) of the PL and PMLG-NH2 adsorbents was a djusted by controlling the ratio of poly(epsilon -lysine), in cross-linking , and the amination conditions (time and ratio of diaminoethane in the part icles), respectively. When adsorption of LPS and acidic protein, e.g. bovin e serum albumin (BSA), by the particles was determined by a batchwise metho d at pH 70 and an ionic strength, mu, of 0.05, they were found to depend st rongly on pK(a,app) but not necessarily on the amino-group content. When pK (a,app) was increased from 6.8 to 8.2, the LPS-adsorbing capacity was incre ased from 1.0 to 2.7 mg mL(-1) wet adsorbent and the apparent dissociation constant for adsorbent and LPS decreased from 3.7 x 10(-10) to 1.0 x 10(-10 ) M. Although PMLG-NH2 with the highest PKa,app, 8.2, had the highest LPS-a dsorbing activity, it also adsorbed BSA. The BSA-adsorbing activity was sha rply reduced when pK(a,app) was reduced to 6.8 or lower. As a result, the c ross-linked PL adsorbent of PKa,app 6.8 had the highest LPS selectivity. Th e adsorbent could reduce levels of natural LPS associated with acidic prote in (ovalbumin or BSA) at pH 70 and mu = 0.05. The residual LPS concentratio n in each sample was > 100 pg mL(-1), and recovery of the protein was >96%.