ABSTRACT
The hemoglobin molecule consists of four polypeptide chains held together by noncovalent attractions. Each contains a heme group and a single oxygen binding site. Hemoglobin A consists of two and two (3chains. The iron ion of the heme can be in the ferrous (Fe2+) or the ferric (Fe3+) oxidation states; the corresponding forms of hemoglobin are called ferrohemoglobin and ferrihemoglobin. Ferrihemoglobin is also called methemoglobin. Only ferrohemoglobin can bind oxygen. The interactions of hemoglobin with O2, CO2 and nitric oxide (NO) take place at the heme iron and the amino termini.
