Interference in protein assays of biological specimens by vanadyl compounds

Vanadyl ribonucleoside and orthovanadate are commonly employed as inhibitors of ribonuclease and protein phosphatase activities, respectively, in a variety of tissue preparations. We have observed that the presence of these agents in the tissue samples interferes in the measurement of their protein content using the Coomassie dye binding procedure. We have demonstrated that this interference in the protein assay can be overcome by including H2O2 at a final concentration of 0.1% in the protein assay medium prior to the addition of the dye reagent. This results in accurate measurements of the protein content in the tissue preparation containing vanadyl ribonucleoside or orthovanadate.