Pk. Kilpatrick et al., SELECTIVE PRECIPITATION OF ANTIBODY WITH LIGAND-MODIFIED PHOSPHOLIPIDS - EFFECT OF LIPID CHAIN-LENGTH, Biotechnology progress, 13(4), 1997, pp. 446-452
The selective precipitation from aqueous solutions of goat polyclonal
anti-biotin antibody (pABA) by complexation with ligand-modified phosp
holipids (LMPs) is described. In this study, the effect of varying the
acyl chain length of the LMP from six to 18 carbon atoms on the rate
and yield of precipitation is detailed. As the acyl chain length incre
ases, the hydrophobic driving force for interaction of ligand-bound an
tibody molecules also increases, resulting in a larger yield of precip
itated antibody. The rate of selective precipitation, however, is obse
rved to pass through a sharp maximum at an acyl chain length of 10-12
carbon atoms. In the range of target antibody and LMP concentrations s
tudied (1-10 mu M), the maximum rates of precipitation are observed fo
r those LMPs in sufficiently low concentrations in aqueous solution to
be below their critical micelle concentration (CMC). The longer chain
length LMPs (12-18 carbon atoms at concentrations of 5-10 mu M) gave
considerably slower rates of precipitation and were all observed to be
micellar solutions. The yield of target antibody as a percentage of a
ntibody precipitated was not observed to pass through a maximum, rathe
r all LMPs with acyl chain lengths longer than 12 carbon atoms were ob
served to give the maximum yield. Thus the optimal structure of an LMP
for precipitation of a target antibody corresponds to the maximum cha
in length (10 carbon atoms) at a concentration level (5-10 mu M) which
still falls below its CMC. The kinetics of precipitation, as monitore
d by measuring turbidity, are well modelled by a theory which combines
the Mie theory of light scattering with the Smoluchowski theory for t
he kinetics of precipitation. The maximum rate constants corresponding
to Smoluchowski kinetics for precipitating pABA were approximately 25
000-30 000 M-1 s(-1) while the maximum yields were 65-70%. The molecu
lar picture which emerges is one in which the optimal rate is obtained
by maximizing hydrophobic driving force for interaction of LMP acyl c
hains while still maintaining a submicellar state of aggregation.