Nonenzymatic radiolabeling of protein by 32P-containing nucleotides

We report a nonenzymatic reaction which results in the radiolabeling of proteins by 32P-containing nucleoside triphosphates. The labeling reaction does not require any cofactors, but is greatly enhanced by the presence of alcohols. Even under optimal conditions, less than 1% of the protein molecules undergo modification. This nonspecific labeling represents a serious artifact which may become significant in systems involving low levels of specific labeling, such as photoaffinity labeling. Since the reaction is not limited to specific proteins, this may, however, provide a simple and rapid procedure for the preparation of labeled proteins.