"The native structure of hemoglobin (Hb) comprises of two α and two β subunits, each of which carries a heme group. There appear to be no previous studies that report the in-vitro folding and assembly of Hb from highly unfolded α and β globin in a 'one-pot' reaction. One difficulty that has to be overcome for studies of this kind is the tendency of Hb to aggregate during refolding. This work demonstrates that denaturation of Hb in 40% acetonitrile at pH 10.0 is reversible." (J Am Soc Mass Spectrum 2007, 18, 8-16) Hemoglobin is ________. A) a tertiary protein with two polypeptides B) a quaternary protein with two polypeptides C) a tertiary protein with four polypeptides D) a quaternary protein with four polypeptide

Hemoglobin is a quaternary protein with four polypeptides. Hemoglobin is comprised of four polypeptides, two alpha chains with 141 amino acid residues and two beta chains with 146 amino acids residues. Hemoglobin is classified as a quaternary protein, because it reaches a quaternary structure when the different polypeptides are attached to each other.