Cl. Stevenson et Mj. Hageman, ESTIMATION OF RECOMBINANT BOVINE SOMATOTROPIN SOLUBILITY BY EXCLUDED-VOLUME INTERACTION WITH POLYETHYLENE GLYCOLS, Pharmaceutical research, 12(11), 1995, pp. 1671-1676
Purpose. The potential to estimate protein solubilities, with limited
protein, by excluded-volume interactions was evaluated using polyethyl
ene glycols (PEG) and recombinant bovine Somatotropin (rbSt). Methods.
Solutions of rbSt were prepared at concentrations significantly below
saturation solubility. Subsequently, varying amounts of PEG were adde
d to force protein precipitation. Following centrifugation, the protei
n concentration in the supernatant was assayed by reversed-phase HPLC,
where a logarithmic relationship between solubility and % PEG was obs
erved. Results. An apparent protein solubility in the absence of PEG w
as determined by extrapolation and compared well with values measured
by conventional approaches. Slopes of log solubility versus % PEG curv
es were consistent with excluded-volume principles and depended on the
molecular weight of the PEG used. Furthermore, the precipitation proc
ess proved to be reversible, allowing for recovery of intact protein.
Solubility-pH profiles obtained in the presence of PEG greatly reduced
the quantities of protein needed and compared favorably with profiles
in the absence of PEG. Conclusions. Thus, it appears feasible and pra
ctical, with certain limitations, to obtain solubility estimates of pr
oteins by volume-exclusion methods with limited supplies of protein.