Iron in heme is linked to globin through

Ans. a (Histidine) (Ref. Harper's biochemistry 27th ed., Chapter 6,12; Harrison's 17th/ pg. 635)Heme, an essentially planar, slightly puckered, cyclic tetrapyrrole, has a central Fe2+ linked to all four nitrogen atoms of the heme, to histidine F8, and, in oxyMb and oxyHb, also to O2.The Hemoglobin:# Heme synthesis:- Occurs in the liver and bone marrow.- Committed step is glycine + succinyl CoA -delta aminolevulinate (ALA Synthase required).- Lead inhibits ALA dehydratase and ferrochelatase, preventing incorporation of iron and causing anemia and porphyria.# Glutathione reductase requires NADPH for its action. In G6PD deficiency NADPH cannot be generated at the normal rate and hence oxidants cannot be destroyed, which in turn cause damage, both to hemoglobin and cell membrane cause hemolysis.# Solubility and reversible oxygen binding, both depend most on the hydrophilic surface amino acids, the hydrophobic amino acids lining the heme pocket, a key histidine in the F helix, and the amino acids forming the a1 b1, and a1 b2 contact points.# Hemoglobin is a tetramer composed of 4 globin molecules; 2 alpha globins and 2 beta globins. The alpha globin chain is composed of 141 amino acids and the beta globin chain is composed of 146 amino acids. Both alpha and beta globin proteins share similar secondary and tertiary structures, each with 8 helical segments (labeled helix A-G).# Each globin chain also contains one heme molecule. Heme, an essentially planar, slightly puckered, cyclic tetrapyrrole, has a central Fe2+ linked to all four nitrogen atoms of the heme, to histidine F8, and, in oxyMb and oxyHb, also to O2 The heme molecule is located between helix E and helix F of the globin protein. The alpha and beta subunits of the globin chains exist in two dimers, which are bonded together strongly. The four Pyrole rings are joined by Methylene or Methylidene bridge (-C = bridge).# In Heme synthesis, the two starting materials are succinyl-CoA and glycine. Pyridoxal phosphate is also necessary in this reaction to "activate" glycine.