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) how many heme groups are present in three hemoglobin protein molecules?