Interpretation of biological and mechanical variations between the Lowry versus Bradford method for protein quantification

BACKGROUND: The identification of differences in protein expression resulting from methodical variations is an essential component to the interpretation of true, biologically significant results. AIMS: We used the Lowry and Bradford methods- two most commonly used methods for protein quantification, to assess whether differential protein expressions are a result of true biological or methodical variations. MATERIAL & METHODS: Differential protein expression patterns was assessed by western blot following protein quantification by the Lowry and Bradford methods. RESULTS: We have observed significant variations in protein concentrations following assessment with the Lowry versus Bradford methods, using identical samples. Greater variations in protein concentration readings were observed over time and in samples with higher concentrations, with the Bradford method. Identical samples quantified using both methods yielded significantly different expression patterns on Western blot. CONCLUSIONS: We show for the first time that methodical variations observed in these protein assay techniques, can potentially translate into differential protein expression patterns, that can be falsely taken to be biologically significant. Our study therefore highlights the pivotal need to carefully consider methodical approaches to protein quantification in techniques that report quantitative differences.