The hemoglobin is phagocytosed by macrophages, and split into its heme and globin portions. Among the most known globular proteins is hemoglobin, a member of the globin protein family. HbF induction is an attempt to reactivate fetal globin gene transcription. Hemoglobin also carries nitric oxide (NO) in the globin part of the molecule. Efforts involve trying to disrupt the fetal globin gene promoter. The amino acid sequences of the globin proteins in hemoglobins usually differ between species. Hemoglobinopathies are simply structural abnormalities in the globin proteins themselves. There also have been studies that show changes in the globin genes. The term globin can refer more specifically to proteins including the globin fold. Instead, it combines with the N-terminal groups on the four globin chains. Globin superfamily members share a common three-dimensional fold.