van den Eijnden-van Raaij A J, de Leeuw A L, Broekhuyse R M
Curr Eye Res. 1985 Jul;4(7):789-92. doi: 10.3109/02713688509020035.
The calcium-binding characteristics of the EDTA-extractable proteins (EEP) from calf lens fiber membranes were studied by equilibrium dialysis and far-ultraviolet circular dichroism measurements. The EEP proteins appeared to contain binding sites with different affinities for calcium. These sites seem to behave as positively cooperating Ca2+ binding sites with a total capacity of 25 mol Ca2+ per mol EEP. The mean apparent dissociation constant (KD) for the Ca2+ binding sites was determined to be 7.7 microM. Calcium binding probably is accompanied by a decrease in the apparent alpha-helical content of the EEP proteins. The present results indicate that the EEP proteins belong to the group of proteins possessing high affinity and binding capacity for calcium. Because of the high calcium-binding capacity, the EEP proteins possibly function as an intracellular calcium store in the lens. The calcium-sensitivity of the conformational state of the EEP proteins, however, might point to a possible regulating function of these membrane proteins in calcium-dependent cellular processes in the lens.
通过平衡透析和远紫外圆二色性测量，研究了小牛晶状体纤维膜中乙二胺四乙酸（EDTA）可提取蛋白（EEP）的钙结合特性。EEP蛋白似乎含有对钙具有不同亲和力的结合位点。这些位点似乎表现为正协同的Ca2+结合位点，每摩尔EEP的总结合容量为25摩尔Ca2+。Ca2+结合位点的平均表观解离常数（KD）测定为7.7微摩尔。钙结合可能伴随着EEP蛋白表观α-螺旋含量的降低。目前的结果表明，EEP蛋白属于对钙具有高亲和力和结合能力的蛋白质组。由于高钙结合能力，EEP蛋白可能在晶状体中作为细胞内钙库发挥作用。然而，EEP蛋白构象状态的钙敏感性可能表明这些膜蛋白在晶状体中钙依赖性细胞过程中具有可能的调节功能。
