Hemoglobin (Hb) is a conjugated protein pigment in red cells, made of heme (iron-tetrapyrrole) and globin (two pairs of polypeptide chains); comprises more than 90% of red cell dry weight.
Normal Hb: adult males 14 to 18 (16 ± 2) g/dL, adult females 12 to 16 (14 ± 2) g/dL.
Structure of Hemoglobin
Heme is a tetrapyrrole ring system terminating in protoporphyrin, with a central iron atom; each globin polypeptide chain is bound to one heme moiety to complete the Hb molecule.
Synthesis of Hemoglobin
Heme forms in mitochondria, globin in ribosomes; iron and protein deficiency causes Hb deficiency, since both are raw materials.
Step 1 Succinyl-CoA (TCA cycle) + glycine → α-amino-β-ketoadipic acid (pyridoxal phosphate) → ALA, via ALA synthase.
Step 2 ALA → porphobilinogen → protoporphyrin-IX.
Step 3 Protoporphyrin-IX + ferrous iron → heme, via heme synthase.