A method for protein assay in Laemmli buffer

A simple, cheap, and rapid assay for soluble and membrane-bound protein solubilized in Laemmli sodium dodecyl sulfate sample buffer is described. Following the addition of trichloroacetic acid to a final concentration of 24%, the induced turbidity was measured at 570 nm in a microplate reader, after an incubation period of approximately 10-30 min. The assay is suitable for measuring bovine serum albumin at a concentration of 15 to 500 micrograms/ml in Laemmli buffer, corresponding to 2 to 75 micrograms protein per well on the microtiter plate. Other nonproteinaceous macromolecules in the sample may introduce an error.