Easy Colorimetric CMC Determination (Detergent accesories) S124   Blue Ball CMC Test Beads

Critical micellar concentration ( CMC ) for a given detergent is very important since it defines the minimal concentration of detergent required to solubilize a hydrophobic molecule , such as a membrane protein. CMC varies with the ionic strength of the buffer, temperature, and detergent used. Measuring CMC can be a time consuming problem. More often than not the literature CMC value is used for a given detergent, then a large excess is used. This excess is a problem during isolation. Recently Brigette Vulliez-Le Normand and Jean-Luc Eisele of the Institut Pasteur have described a fabulous simple colorimetric CMC determination method which makes it easy to determine how much detergent to add to your membrane protein extraction buffer. Briefly, test solutions are prepared containing varying amounts of detergent. The test solution is treated with a blue hydrophobic test piece. A blue color is evident. If one plots the absorbance of hydrophobic blue dye solubilized at 612 nanometers on a micro-well reader, a graph of two intersecting lines results with the exact CMC equal to the amount of detergent at the point of intersection. In fact the test can be “eye balled� with very good accuracy. The real beauty of the Vulliez-Le Normand and Eisele method is that one can visually determine an optimal concentration of detergent to employ in extracting a membrane protein and obtain visual feedback regarding optimal time for extraction. The method is versatile in that it works well with steroid based detergents such as CHAPS and CHAPSO, deoxycholate and cholate as well as non-steroid detergents like ?-octylglucoside. Soltec Bioscience has provided a kit to make an easier determination. The dye is loaded onto uniform beads. Simply place on of the blue balls into the well of a micro-well strip or test tube and incubate with your test solution. Normally four to five data point below and above the CMC is sufficient for the determination of optimal detergent concentration.