Solubility of protein complexed with galloylglucoses

Solubility of bovine serum albumin (BSA) (P) precipitated with tetragalloylglucose (T) was investigated by successive washing over the pH range of 3-7. The solubility was highly dependent on pH (4<5<6<7<3), and these results were comprehensible with the interrelation between TP ratio required for the precipitation [T/P(R)] and number of the strong binding sites on a BSA molecule (NSB); when NSB > T/P(R) (pH 4 and 5), the precipitates were very stable, while when NSB < T/P(R) (pH 3, 6 and 7), precipitated BSA was easily solubilized by washing. Galloylglucose structure also affected the solubility of the precipitates at pH 4 (penta- < tetra- < 2,3,6-tri- < 2,3,4-tri-galloylglucose). These differences were explainable mainly with their NSBs, which increase dramatically with an increase in the number of galloyl groups in a galloylglucose molecule [35(penta) > 15(tetra) > 0(tri)]. (C) 1997 Elsevier Science Ltd.