  the bradford protein assay is a spectroscopic analytical procedure used to measure the concentration of protein in a solution. it is subjective, i.e., dependent on the amino acid composition of the measured protein. the bradford protein assay was developed by marion m. bradford. ==principle== thumb|200px|right|test tubes containing bradford reagent alone (left) and with lysozyme added (right) the bradford assay, a colorimetric protein assay, is based on an absorbance shift of the dye  coomassie brilliant blue g-250 in which under acidic conditions the red form of the dye is converted into its bluer form to bind to the protein being assayed. during the formation of this complex, two types of bond interaction take place: the red form of coomassie dye first donates its free electron to the ionizable groups on the protein, which causes a disruption of the protein's native state, consequently exposing its hydrophobic pockets. these pockets in the protein's tertiary structure bind non-covalently to the non-polar region of the dye via van der waals forces, positioning the positive amine groups in proximity with the negative charge of the dye. the bond is further strengthened by the ionic interaction between the two. the binding of the protein stabilizes the blue form of the coomassie dye; thus the amount of the complex present in solution is a measure for the protein concentration, and can be estimated by use of an absorbance reading. the (bound) form of the dye has an absorption spectrum maximum historically held to be at 595 nm. the cationic (unbound) forms are green or red. the binding of the dye to the protein stabilizes the blue anionic form. the increase of absorbance at 595&nbsp;nm is proportional to the amount of bound dye, and thus to the amount (concentration) of protein present in the sample. unlike other protein assays, the bradford protein assay is less susceptible to interference by various chemicals that may be present in protein samples. an exception of note is elevated concentrations of detergent. sodium dodecyl sulfate (sds), a common detergent, may be found in protein extracts because it is used to lyse cells by disrupting the membrane lipid bilayer. while other detergents interfere with the assay at high concentration, the interference caused by sds is of two different modes, and each occurs at a different concentration. when sds concentrations are below critical micelle concentration (known as cmc, 0.00333%w/v to 0.0667%) in a coomassie dye solution, the detergent tends to bind strongly with the protein, inhibiting the protein binding sites for the dye reagent. this can cause underestimations of protein concentration in solution. when sds concentrations are above cmc, the detergent associates strongly with the green fo
Analytical_chemistry Chemical_tests Protein_methods