Department of Clinical Biochemistry, School of Medicine, Tehran, Iran.
Anal Biochem. 2013 Mar 15;434(2):287-91. doi: 10.1016/j.ab.2012.11.014. Epub 2012 Dec 3.
The Bradford protein assay is a popular method because of its rapidity, sensitivity, and relative specificity. This method is subject to some interference by nonprotein compounds. In this study, we describe the interference of cetyltrimethylammonium bromide (CTAB) with the Bradford assay. This interference is based on the interaction of Coomassie Brilliant Blue G-250 (CBB) with this cationic detergent. This study suggests that both electrostatic and hydrophobic interactions are involved in the interaction of CTAB and CBB. The anionic and neutral forms of CBB bind to CTAB by electrostatic attraction, which accelerates hydrophobic interactions of these CBB forms and the hydrophobic tail of CTAB. Consequently, the hydrophobic regions of the dominant free cationic form of CBB dye compete for the tail of CTAB with two other forms of the dye and gradually displace the primary hydrophobic interactions and rearrange the primary CBB-CTAB complex. This interaction of CTAB and CBB dye produces a primary 650-nm-absorbing complex that then gradually rearranges to a complex that shows an absorbance shoulder at 800-950 nm. This study conclusively shows a strong response of CBB to CTAB that causes a time-dependent and nearly additive interference with the Bradford assay. This study also may promote an application of CBB for CTAB quantification.
考马斯亮蓝 G-250（CBB）与这种阳离子去污剂的相互作用基于以下原理：CTAB 与 CBB 之间存在静电和疏水相互作用。CBB 的阴离子和中性形式通过静电吸引与 CTAB 结合，这加速了这些 CBB 形式和 CTAB 疏水尾之间的疏水相互作用。结果，CBB 染料的主要游离阳离子形式的疏水区域与染料的另外两种形式竞争 CTAB 的尾部，并逐渐取代主要的疏水相互作用并重新排列主要的 CBB-CTAB 复合物。CTAB 和 CBB 染料的这种相互作用产生了最初的 650nm 吸收复合物，然后逐渐重新排列为在 800-950nm 处显示吸收肩的复合物。该研究明确表明 CBB 对 CTAB 具有强烈的响应，导致与 Bradford 测定法的时间依赖性和几乎加性干扰。本研究还可能促进 CBB 用于 CTAB 定量。
