Detergent interference with Lowry assay of bovine milk fat globule membrane protein

The interference of Triton X-100, Lubrol PX, and Zwittergent 3-14 detergents with the determination of bovine milk fat globule membrane protein by the Lowry protein assay was examined. In the concentration range of 0.5 to 2.0% (w/v), all three detergents caused concentration-dependent overestimates of protein content of both bovine serum albumin and bovine milk fat globule membrane samples. This detergent concentration range is an important operational concentration range for the solubilization of membrane proteins. When sodium dodecyl sulfate (SDS) was added to yield a 1:1 concentration ratio of SDS:interfering detergent, the overestimates of Lowry protein in the presence of all three detergents were eliminated.