Protein Content Quantification by Bradford Method

Abstract

There are many procedures to quantify the protein content of an extract. A single protein solution would probably throw different results if measured with different methods, because they are based on different principles. Actually an absolute method does not exist; everyone has some advantages and disadvantages. The choice of an adequate method will depend on the nature of the proteins present in the sample, on the purity of the extracts, on the required sensibility and accuracy, and on the desired speed (Boyer, 1986). The most widely utilised methods for the analysis of protein contents are the assays of Biuret, Bradford, Kjendahl, Lowry, Smith, and Warburg-Christian. Nonetheless, many authors recommend the spectrophotometric assay of Bradford (1976) because of its multiple advantages if compared with other methods (Snyder and Desborough, 1978; Berges et al., 1993; and see Bio-Rad bulletin 1069EG, 1979). The most conspicuous advantages of Bradford method are: (i) the use of a single reactive, (ii) the rapidity of the reaction (just 5 min.), (iii) a high stability of the protein-dye complex, (iv) a high reproducibility, and (v) the occurrence of minimal interferences. This simple, fast, and inexpensive method has multiple applications in experimental sciences. Besides being a well-suited method for repetitive determination of protein concentrations (e.g., in physiological, inmunological, cytological, clinical, and food quality routine analysis), the Bradford assay is often coupled to other techniques. It is a convenient 283 M.J. Reigosa Roger, Handbook of Plant Ecophysiology Techniques, 283-295.