Colorimetric measurement of protein stained with coomassie brilliant blue R on sodium dodecyl sulfate-polyacrylamide gel electrophoresis by eluting with formamide.

Proteins separated by polyacrylamide gel electrophoresis (PAGE) are usually detected by staining. In general, the proteins are measured by densitometric scanning or by eluting the dye and reading in a colorimeter. Racusenr eported a methodfor quantitative color measurement consisting in eluting Amido Black 10B with 1 n NaOH. Coomassie Brilliant Blue R-250 (CBB-R) is widely used for staining because of its high sensitivity. Recently, Tal et al.2) reported that CBB-Rbound to protein on polyacrylamide gel (PAG) is eluted with dimethylsulfoxide. We found that CBB-R is quantitatively extracted with formamide from PAGcontaining sodium dodecyl sulfate (SDS) and can be measured spectrophotometrically.3) In this paper, we describe a simple method for this quantitative colorimetric measurement. The slab-PAGE system was purchased from Atto Corp., Tokyo, Japan (SJ-1600 SD type). CBB-R was obtained from Fluka AG, Buchs, Switzerland, and all other reagents for PAGE and standard proteins were from WakoPure Chemicals,