Figure 1: SDS-PAGE of formaldehyde-fixed RNase A before and after protein retrieval. Lane M: molecular weight marker; lane 1: native RNase A; lane 2: formaldehyde-fixed RNase A after the removal of excess formaldehyde; lane 3: formaldehyde-fixed RNase A sample from lane 2 after retrieval in 20 mM Tris HCl, pH 4.0, with 2% SDS; lanes 4, 6, and 8: formaldehyde-fixed RNase A after incubation in 100% ethanol for 1 hr, 24 hr or 1 week, respectively; lanes 5, 7, and 9; 1 hr, 24 hr or 1week formaldehydefixed, ethanol-treated RNase A after retrieval in 20 mM Tris HCl, pH 4.0, with 2% SDS. The RNase A samples were heated at 100°C for 20 min, followed by 60°C for 2 hr.