prehemoglobin

Prehemoglobin is a term sometimes encountered in older or nonstandard biochemical literature to denote precursor forms in the biosynthesis and assembly of hemoglobin before it becomes a functional molecule. The term is not widely used in modern science, and when it appears it is often used to describe transient intermediates in hemoglobin formation.

In discussions where prehemoglobin is mentioned, it is commonly used to refer to immature forms such as aphemoglobin—the globin protein without its heme prosthetic group—and other partially assembled forms. Some sources have described a so-called prohemoglobin stage as a heme-containing intermediate that has not yet formed the mature tetrameric structure of hemoglobin. Modern terminology tends to distinguish clearly between the globin polypeptides (alpha and beta chains), the heme prosthetic group, and the assembled holoprotein (hemoglobin).

Biogenesis of hemoglobin involves several coordinated steps. Globin mRNAs are translated in developing erythroid cells to produce the alpha and beta globin chains. Heme is synthesized separately in mitochondria and cytosol. Heme is then inserted into apoglobins to form hologlobins, and the alpha and beta subunits assemble into the functional tetramer HbA in adults (and HbF in fetuses). The concept of prehemoglobin and related intermediates reflects transient stages prior to full assembly and oxygen-carrying function.

Clinical relevance for the term prehemoglobin is limited, since it is not a standard clinical or diagnostic category. Hemoglobin disorders are typically described in terms of globin gene mutations (thalassemias), defects in heme biosynthesis (porphyrias), or errors in hemoglobin assembly, rather than in relation to a prehemoglobin state. See also: hemoglobin, globin, heme, erythropoiesis.