Measurement of detergent concentration using 2,6-­dimethylphenol in membrane-protein crystallization

Methods have previously been developed to measure detergent concentration in membrane-protein samples, but most have significant limitations, such as requiring specialized equipment or consuming a significant amount of precious sample. This work explores the use of 2,6-dimethylphenol in a phenol-sulfuric acid assay to accurately measure the concentration of common glycosidic-based detergents used in crystallization. This method is amenable to routine laboratory use, provides excellent sensitivity and significantly reduces the sample volume required. Using an Escherichia coli tyrosine kinase (Etk) construct as an example, it is shown that the crystallization potential of Etk is directly influenced by measurable changes in detergent concentration.