51Why does the Bradford assay respond differently to different proteins?52What is the basic principle of the Lowry assay?53Why do colorimetric protein assays require a standard curve?54What might cause a flattened spectral peak?55Why can absorbance be negative?56What should I check for a jagged spectrum or large differences between repeats?57Why can different instruments give different results for the same sample?58Is OD600 truly absorption?59How can OD600 be converted to cell count?

What is the basic principle of the Lowry assay?

Copper first reacts with peptide bonds, after which protein-associated groups reduce the Folin–Ciocalteu reagent to develop color.