True statement about hemoglobin is

The red colouring matter of the blood is a conjugated protein, Haemoglobin, a chromoprotein, containing haem as prosthetic group and globin as the protein pa-apoprotein. Haem-containing proteins are characteristic of the aerobic organisms and are altogether absent in anaerobic forms of life. The normal concentration of Hb in an adult male varies from 14.0 to 16.0 gms% and there are about 750 gms of Hb in the total circulating blood of a 70 kg man. Approximately 6.25 Gm (90 mg/kg) of Hb are produced and destroyed in the body each day. The structure of Haem remains the same in Hb from any animal source, the basic protein globin varies from species to species in its amino acid composition and sequence and thus responsible for the species-specificity. The polypeptide chains of globin of adult Hb, are characterized by a relatively high content of histidine (His) and lysine (Lys) and a small amount of isoleuciene (Ile). By means of isotopic `tracer&; techniques, it has been shown that the polypeptide chains are formed from amino acids derived from dietary proteins. Globin Studies of globin, the protein pa of Hb, have revealed that it is composed of four polypeptide chains, two identical a-chains, and two identical b-chains, in normal adult Hb, arranged in the configuration of a `tetrahedron&;. Thus there are six edges of contact. Polypeptide Chains: Each polypeptide chain contains a `haem&;, in the so-called haem-pocket. Thus one Hb molecule contains four haem units.Ref: Textbook of medical biochemistry, MN Chatterji, 8th edition, page no: 150