Identification of denatured enzyme proteins in sodium dodecyl sulfate polyacrylamide gels

A simple modification of the immunological sandwich method of Muilerman et al. (4) for the identification of denatured enzyme proteins in sodium dodecyl sulfate-polyacrylamide gels is described, enabling the method to be used in principle for any enzyme whose activity is not inhibited by binding to antibodies. An immunological sandwich consisting of denatured enzyme, antibodies, and native enzyme is formed on a nitrocellulose filter blot of the gel, the filter is divided into strips, and each strip is tested for enzyme activity. The presence of enzyme activity serves to identify the region in the gel containing denatured enzyme protein. Experiments with human lysosomal α-glucosidase as a model system are described. The method was applied to identify a protein of M_r 125,000 as the main component with UDPgalactose pyrophosphatase activity in a partially purified preparation of the enzyme from rat liver.