Visualization of sialoglycoproteins in polyacrylamide gels by acidic ninhydrin reaction

A new method for staining sialoglycoproteins in polyacrylamide gel after disc electrophoresis is described. The method utilizes the reaction of sialic acids with an acidic ninhydrin reagent which yields a stable color with an absorption maximum at 470 nm. After electrophoresis, the polyacrylamide gel is placed in a test tube and heated with 5 ml of the acidic ninhydrin reagent for 10 min in a boiling water bath. Sialoglycoproteins are detected as brown bands. No additional procedure such as destaining is necessary. When 20 micrograms fetuin, a sialoglycoprotein, per gel is applied, the band remains visible for at least 2 h. Stained gel can be scanned with a gel scanner at 470 nm. When the stained gel was dried on a sheet of polypropylene filter, the color was stable for at least one month. The present method is superior to the method using Stains-all (3,3'-diethyl-9-methyl-4,5,4',5'-dibenzothiacarbocyanine) in specificity and simplicity for the detection of sialoglycoproteins.