Solubilization of SCD and SCDP. DSIMs were treated with detergent (final concentration, 2%, as described in MATERIALS AND METHODS). Insoluble proteins were removed by ultracentrifugation. The detergent extracts were incubated overnight at 37°C. Controls were frozen at −20°C overnight. The solubilized proteins were separated by SDS-PAGE and visualized by staining with Coomassie blue. (A) The samples analyzed were unfractionated DSIMs (lane 1), CHAPS-soluble DSIMs at −20°C (lane 2) and 37°C (lane 3), TX100-soluble DSIMs at −20°C (lane 4) and 37°C (lane 5), digitonin-soluble DSIMs at −20°C (lane 6) and 37°C (lane 7), and deoxycholate/TX100 (1:1)-soluble DSIMs at −20°C (lane 8) and 37°C (lane 9). The 37-kDa SCD protein band is marked by an asterisk in lanes 1 and 8. The positions of molecular mass markers (kilodaltons) are shown on the right. (B) Enlarged image of the bottom half of lanes 8 and 9. The 37-kDa SCD band is marked by an asterisk on the left. The positions of molecular mass markers (kilodaltons) are indicated on the right.