Ultramicrodetection of proteins in polyacrylamide gels

Here we report the development of a highly sensitive procedure to detect proteins within separation matrices which should facilitate the characterization of rare proteins. The procedure is based on photochemical reactions where very low amounts of silver are deposited around proteins and in a series of steps are converted to silver sulfide. When this conversion is carried out in the presence of [35S]thiourea the resulting radioactive silver sulfide allows detection down to femtogram quantities of protein. In this work we applied the above principle to proteins separated on sodium dodecyl sulfate-polyacrylamide gels, thus not influencing physical and chemical parameters which are important for separation. This procedure should find application in any technique where detection of very low or limited amounts of proteins are required.