Iron deposition and morphology on EM of SOD2-deficient red cells. (A) Modified Perl stain of peripheral blood from recipients of Sod2^+/+ or Sod2^–/– fetal liver transplants (as a source of hematopoietic stem cells) demonstrating excess iron on SOD2-deficient cells. (B) Electron micrographs of Sod2^+/+ and Sod2^–/– reticulocytes reveal an increased number of mitochondria with prominent intramitochondrial membranes in SOD2-deficient cells. No obvious foci of iron deposition (electrondense material) were seen within SOD2-deficient cells with standard EM processing. (C) Electron micrographs of reticulocytes prestained with potassium ferricyanide prior to processing. Small arrows show diffuse electron-dense deposits in matrix of mitochondria, and large arrows show strong electron-dense deposits in the outer mitochondrial membrane of Sod2^–/– cells. Bar length is 500 nm.