1.2 Determination of the atomic structure of hemoglobin A (from normal adult) is very revea ling. 1. 2. 1 The protein molecule exists as a a2, tetramer 1. 2.2 Each subunit has a structure strikingly and unexpectedly similar to each other and to that of myoglobin, indicating quite different amino acid sequences can specify very similar 3-D structures 1.2. 3 Extensive interactions exist between the unlike subunits through noncovalent interactions 1.2.4 Quaternary structure changes markedly when O2 binds Crystals of deoxyhemoglobin shatter (break when exposed to O2. 2.50, binds to the sixth coordination position of the ferrous iron(as in myoglobin).1.2 Determination of the atomic structure of hemoglobin A (from normal adult) is very revealing. 1.2.1 The protein molecule exists as a a2b2 tetramer. 1.2.2 Each subunit has a structure strikingly and unexpectedly similar to each other and to that of myoglobin, indicating quite different amino acid sequences can specify very similar 3-D structures. 1.2.3 Extensive interactions exist between the unlike subunits through noncovalent interactions. 1.2.4 Quaternary structure changes markedly when O2 binds. Crystals of deoxyhemoglobin shatter (break) when exposed to O2 . 1.2.5 O2 binds to the sixth coordination position of the ferrous iron (as in myoglobin)