Purification, amino terminal analysis, and peptide mapping of proteins after in situ postelectrophoretic fluorescent labeling

Fluorescein uptake by a monocarboxylic acid transporter in human intestinal Caco-2 cells

The fluorescein transport characteristics of the human intestinal epithelial Caco-2 cell line were examined in monolayer cultures. The initial uptake rate was concentration-dependent and saturable; the Michealis constant and the maximum velocity were 0.40 mM and 1.32 nmol/min/mg protein, respectively. A protonophore, carbonyl cyanide m-chlorophenyl-hydrazone, reduced uptake significantly. The replacement of extracellular sodium ions by lithium ions did not alter the initial uptake rate. These facts imply that the transport is driven by a proton gradient. The initial uptake rate was strongly dependent upon extracellular pH, and the uptake was optimal at approximately pH 5.5. Based on the protolytic constants, the main species of fluorescein in the pH range of 5.5 to 6.0 was calculated to be a monoanion, suggesting that fluorescein was taken up by Caco-2 cells as a monocarboxylate. The following findings support this conclusion: the uptake was inhibited significantly by monocarboxylate compounds such as salicylate and pravastatin, but not by di- or tricarboxylic acids or by acidic amino acids. Furthermore, salicylate-preloaded cells showed remarkably enhanced uptake of fluorescein, indicating that monocarboxylates and fluorescein share a common transport carrier. The transporter has a wide spectrum of substrate recognition and seems likely to be different from MCT1.

Mixed-dye staining method for protein detection in polyacrylamide gel electrophoresis using calconcarboxylic acid and rhodamine B

We have developed a new mixed-dye protein staining method that is simple, rapid, and sensitive. A freshly prepared mixture of calconcarboxylic acid (NN, 0.02%) and rhodamine B (RB, 0.04%) in 40% methanol/7% acetic acid, was used as a staining solution. RB acts as an auxiliary agent to inhibit the binding of NN to the gel matrix, reducing the background staining and therefore enhancing the protein staining by NN. This mixed-dye staining method reduces the total staining and destaining time to less than an hour, and increases the sensitivity to 25 ng of bovine serum albumin, which is greater than the 100 ng sensitivity limit of Coomassie Brilliant Blue R-250 (CBBR) staining.

Comparison of different staining methods for polyvinylidene difluoride membranes

Several new staining methods for polyvinylidene difluoride membranes, including mercurochrome, silver and dimethylaminoazobenzene isothiocyanate staining were compared with Coomassie Brilliant Blue and gold staining. Of these, Coomassie was most versatile and completely compatible with ensuing microsequencing, immunostaining or other visualization methods, while gold and silver staining were more sensitive. Mercurochrome allows selective detection of sulfhydryl-containing proteins while dimethylaminoazobenzene isothiocyanate staining may allow quantitation of sequenceable protein.