Interference of sugars in the Coomassie Blue G dye binding assay of proteins.

The presence of sugars causes significant deviation from the actual absorbance of proteins in the Bradford protein assay. In these studies, polysaccharides and disaccharides at milligram levels mimicked proteins in microgram equivalents. Monosaccharides, which individually did not show any absorbance, interfered significantly by sequestering the dye species. The studies demonstrated that in a mixture of sugars and proteins, sugar interference was much higher than expected from sugar molecules' individual contribution. Estimated protein values were increased 2 to 4 times after precipitation from fungal culture broths. Thus, in carbohydrate-rich samples, protein concentrations should be ascertained by precipitation from crude extracts and resolubilization in a noninterfering buffer.