Detection of beta-glucosidase activity on sodium dodecyl sulphate-polyacrylamide gels.

Maize beta-glucosidase (beta-D-glucoside glucohydrolase, EC 3.2.1.21) was incubated in the presence of SDS concentrations varying from 0.025 to 3.2% at two different pHs (5 and 8), electrophoresed through 10% SDS-polyacrylamide gels, and stained for activity. The zymogram patterns of SDS-treated samples were similar to those of untreated (control) samples. The same samples were also analyzed by native PAGE and IEF, yielding similar patterns for controls and for SDS-treated samples. However, zymogram patterns were severely distorted on IEF gels when SDS concentration of the sample medium was at or above 1.6%. These results suggest that the beta-glucosidase monomer (a 60 kD polypeptide) is either catalytically active or it re-forms dimers upon the removal of SDS during equilibration washes, since the in vivo form of the functional enzyme is thought to be a dimer. The activity of maize beta-glucosidase on SDS-gels after SDS-PAGE does not seem to be limited to this enzyme alone, because beta-glucosidases from other sources (e.g., almond, Trichoderma, and Penicillium) were also active on SDS-gels. Enzyme activity in the presence of SDS or after SDS treatment may be more common than one would expect on the basis of the conventional biochemical dictum that ionic detergents denature and inactivate enzymes. Enzyme activity in the presence of SDS and development of zymograms on SDS-gels offer new approaches to studies of enzyme structure and activity.