Bio-Rad Quick Start™ Bradford Protein Assay - Manual (Page 4)

Brilliant Blue G-250 dye to proteins (Bradford
1976). The dye exists in three forms: cationic
(red), neutral (green), and anionic (blue) (Compton
and Jones 1985). Under acidic conditions, the
dye is predominantly in the doubly protonated red
cationic form (A
max
= 470 nm). However, when the
dye binds to protein, it is converted to a stable
unprotonated blue form (A
max
= 595 nm) (Reisner
et al. 1975, Fazekes de St. Groth et al. 1963,
Sedmack and Grossberg 1977). It is this blue
protein-dye form that is detected at 595 nm in the
assay using a spectrophotometer or microplate
reader.
H + H +
Cation « Neutral form « Anion
470 nm (red) 650 nm (green) 595 nm (blue)
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