Streptozotocin (STZ), urea, thiourea, sodium dodecyl sulfate (SDS), 3-((3-cholamidopropyl) dimethylammonio)-1-propanesulfonate (CHAPS), 2-mercaptoethanol (2-ME), dithiothreitol (DTT), bromophenol blue, iodoacetamide, RNase A, and DNase I were purchased from Wako Pure Chemical Industries, Ltd. (Osaka, Japan). Source information for all other assay reagents and materials is stated in the Materials and Methods section described below.