Sensitive protein assay in presence of high levels of lipid

This chapter describes a method that is capable of accurately measuring low amounts of a protein in the presence of very high levels of lipid. This procedure was developed from the amido black 10 B methods of Schaffner and Weissmann and Newman et al. and incorporates several critical modifications that enable an assay to be performed with lipid-containing samples without any interference. One approach has been to remove an interfering lipid by extraction with organic solvents. However, because certain proteins display a limited solubility in such solvents, this strategy often fails. Another widely used approach involves the inclusion of sodium dodecyl sulfate (SDS) in a modified Lowry procedure to reduce lipid (and detergent) interference. As oxidized lipid continues to react to produce a substantial amount of color in the Lowry assay and as most lipid samples are partially oxidized, this procedure is not suitable for the accurate measurements of a protein in samples containing excess of lipid.