text: The Hill equation was first used to describe the cooperative binding of this protein.
full_question: The Hill equation was first used to describe the cooperative binding of this protein. The fetal form of this protein has a higher affinity than its adult form because it does not interact with 2,3-BPG ["two three b-p-g"]. This protein shows a lower binding affinity under acidic conditions and in higher carbon dioxide concentrations, a phenomenon known as the Bohr shift. This protein consists of two alpha and two beta subunits, and like catalase it contains four porphyrin rings with iron centers. This protein has a higher affinity to carbon monoxide than its typical substrate, oxygen. For 10 points, name this protein found in red blood cells.
first_sentence: The Hill equation was first used to describe the cooperative binding of this protein.
raw_answer: hemoglobin [or Hb]