Advantages of picrate fixation for staining polypeptides in polyacrylamide gels

When acetic acid-urea polyacrylamide gels with or without Triton X-100 were immersed in 0.1 M Na picrate, pH 7, to which 1/4 vol Coomassie blue staining solution (0.2% in 45% methanol, 10% acetic acid, 45% water) was added, proteins stained rapidly (within a few minutes in gels without Triton and within an hour in gels with Triton) with little or no background staining. Thus protein bands could be observed in a single step with no destaining. The picrate-Coomassie blue method fixed and stained a small peptide (bradykinin, nine amino acids) that was not observed in gels stained with fast green, silver, or Coomassie blue following fixation in 50% trichloroacetic acid. The picrate-Coomassie blue method gave high-contrast bands suitable for densitometry. Gels containing sodium dodecyl sulfate were also stained by the picrate-Coomassie blue method if they were first washed briefly (1 h) in 45% methanol, 10% acetic acid, 45% water, presumably to remove the detergent. These gels also stained rapidly with almost no background.