DPPH radical scavenging activity and dot blot assay of MT-I and MT-II proteins from sweet potato tuberous roots. MT-I and MT-II proteins were tested for scavenging activities of DPPH radical (A). Glutathione was used as a positive control. Dot blot assay on a silica sheet stained with a DPPH solution in methanol (B). From left to right dots are: Each 3 μL plant extract (200, 100, 50, 25, and 12.5 μg/mL protein) applied from leaf to right. Each 3 μL GSH (10, 5, 2.5, 12.5, and 6.25 μg/mL) applied from left to right.