A human mitochondrial ferritin, MtF, was found to express as a pro-protein. When a mitochondrion takes it up, it processes it into a mature protein similar to the ferritins found in the cytoplasm, which it assembles to form functional ferritin shells. Unlike other human ferritins, it appears to have no introns in its genetic code. An X-ray diffraction study has revealed that its diameter is 1.70 angstroms (0.17 nm), it contains 182 residues, and is 67% helical. The mitochondrial ferritin's Ramachandran plot shows its structure to be mainly alpha helical with a low prevalence of beta sheets.