BSA is normally prepared as a 3% dilution in PBS-T or TBS-T. There can however be issues with contamination from native immunoglobulins which can cause issues with cross-reactivity. Alkaline phosphatase antibodies can also be inhibited by some preparations of milk alongside biotin labelled antibodies being interfered with by the milk preparation.īSA is also widely used as it is suitable for all detection systems as it does not contain biotin or phosphopeptides. Milk based blocking solutions should not be used for any experiments involving phosphorylation specific antibodies due to the presence of casein which is a phosphoprotein that can interfere with detection. Due to the rapid growth of microbial contamination milk based solutions should be made up fresh for every application. Some preparations contain sodium azide as a preservative although it should be noted that azide can inhibit horseradish peroxidase, the most commonly used secondary antibody conjugate in western blots. The most commonly used blocking solution is a solution of 5% non-fat dry milk in PBS-T which works well for the vast majority of applications at a inexpensive price. Comparison between commonly used blocking buffers in western blotting. Contains immunoglobulins and serum proteins that can cross-react with the primary or secondary antibody.Incompatible with some anti-immunoglobulin antibody detection.Different sized proteins therefore require different formulations of acrylamide gel to get optimum separation (figure 1). Polyacrylamide gels are a matrix of cross-linked acrylamide monomers with the tightness of the mesh dependent upon the amount of acrylamide and cross-linker present. In a SDS page all proteins are denatured and have a uniform negative charge applied to them therefore migration is due to differences in size. What loading controls should be included to account for variability in loading and transfer ( see section 2.3)Ģ.1 Choosing an acrylamide gel percentage 2.1.1 Single concentration gels.What blocking solution to use for the experimental conditions ( see section 2.2).What percentage acrylamide gel to use in order to get the best separation ( see section 2.1).Proteins are separated by their mass before being transferred onto a membrane (either PDVF or nitrocellulose) and probed with antibodies to reveal expression of specific proteins.īefore starting any western blot experiment it is important to consider the following points: Proteins are first denatured before being loaded onto an acrylamide gel with an electric current applied. Western blotting, also known as immunoblotting, is a key technique in molecular biology to investigate changes in protein expression in a range of different tissue types. 2.1 Choosing an acrylamide gel percentageĢ.4 Selecting appropriate loading controlsĥ.1 Measuring the molecular weight of a proteinĥ.2 Quantifying protein expression from an immunoblot

Imagej quantification western blot