An improved Bradford protein assay for collagen proteins

A modification of the protein determination method of Bradford adapted for collagen-rich samples is described. The use of Coomassie-based protein determination methods is limited by the great variation in colour yield obtained for different proteins. This is especially important in samples containing significant amounts of collagen where direct application of the methods of Lowry and Bradford results in underestimated values. Addition of small amounts of sodium dodecyl sulphate (SDS) (0.0035%) to the diluted solutions of Coomassie Brilliant Blue G used as dye reagent in the Bradford colorimetric assay caused a 4-fold increase in the colour response of three collagen proteins (Col I, III and IV) and a decrease in absorbance for various non-collagen proteins. The presence of SDS in the reagent did not result in a significant metachromatic shift of the collagen-dye complexes. This simple modification in the preparation of the reagent for the Bradford assay allows similar response curves to be obtained for collagen and non-collagen proteins, making the modified assay of potential use for protein determination in collagen-rich samples such as pancreatic extracts.