Fonterra Research and Development Centre, Private Bag 11029, Dairy Farm Road, Palmerston North, New Zealand.
Van 't Hoff Laboratory for Physical and Colloid Chemistry, Padualaan 8, Utrecht University, The Netherlands; NIZO Food Research, PO Box 20, 6710 BA Ede, The Netherlands.
J Colloid Interface Sci. 2014 Sep 15;430:214-20. doi: 10.1016/j.jcis.2014.05.036. Epub 2014 Jun 2.
Oppositely charged proteins should interact and form complex coacervates or precipitates at the correct mixing ratios and under defined pH conditions.
The cationic protein lactotransferrin (LF) was mixed with the anionic protein β-lactoglobulin (B-Lg) at a range of pH and mixing ratios. Complexation was monitored through turbidity and zeta potential measurements.
Complexation between LF and B-Lg did occur and complex coacervates were formed. This behaviour for globular proteins is rare. The charge ratio's of LF:B-Lg varies with pH due to changing (de) protonation of the proteins. Nevertheless we found that the complexes have a constant stoichiometry LF:B-Lg=1:3 at all pH's, due to charge regularization. At the turbidity maximum the zeta potential of complexes is close to zero, indicating charge neutrality; this is required when the complexes form a new concentrated liquid phase, as this must be electrically neutral. Complexes were formed in pH region 5-7.3. On addition of salt (NaCl) complexation is diminished and disappears at a salt concentration of about 100 mMol. The coacervate phase has a very viscous consistency. If we consider the proteins as colloidal particles then the formed complex coacervate phase may have a structure that resembles a molten salt comparable to, for example, AlCl3.
带相反电荷的蛋白质在正确的混合比例和特定的 pH 条件下应该相互作用并形成复杂凝聚物或沉淀物。
将阳离子蛋白乳转铁蛋白 (LF) 与阴离子蛋白β-乳球蛋白 (B-Lg) 在一系列 pH 值和混合比例下混合。通过浊度和动电电位测量来监测络合情况。
LF 和 B-Lg 之间确实发生了络合，形成了复杂凝聚物。这种行为在球状蛋白中很少见。由于蛋白质的（去）质子化作用，LF:B-Lg 的电荷比随 pH 值而变化。尽管如此，我们发现由于电荷规整化，复合物在所有 pH 值下都具有恒定的化学计量比 LF:B-Lg=1:3。在浊度最大值处，复合物的动电电位接近零，表明电荷中性；当复合物形成新的浓缩液相时，必须保持电中性，这是必需的。复合物在 pH 5-7.3 区域形成。添加盐（NaCl）后，络合作用减弱，并在约 100mMol 的盐浓度下消失。凝聚相具有非常粘稠的一致性。如果我们将蛋白质视为胶体颗粒，那么形成的复杂凝聚相可能具有类似于熔融盐的结构，例如 AlCl3。
