| Abstract: | Electrophoretically and ultracentrifugally homogeneous glutamic acid decarboxylase purified from mouse brain showed multiple protein bands after electrophoresis in SDS polyacrylamide gel. The positions and intensities of the multiple bands were constant despite different treatments of the enzyme with various concentrations of SDS, β-mercaptoethanol, and urea at different temperatures. The major band had an apparent molecular weight of approximately 60,000 daltons and there were three minor bands of molecular weights, about 120,000, 90,000, and 75,000 daltons, respectively. The molecular weights of almost all bands were approximately integral multiples of 15,000. The possible subunit structure of this enzyme has been discussed in the light of the latter data and data previously reported from ultracentrifugation and gel filtration studies. We suggest that this enzyme may be a hexamer consisting of 15,000-dalton sub-units and that dissociation of these sub-units in SDS is accompanied by reassociation into a variety of aggregates, the probability of whose formation is determined by structural features that are more important than the differences encountered under the environmental conditions employed in these studies. |
