The protomers associate to form a larger oligomer of two or more copies of this unit.
The term was introduced by Chetverin[1] to make nomenclature in the Na/K-ATPase enzyme unambiguous.
In chemistry, a so-called protomer is a molecule which displays tautomerism due to position of a proton.
[2][3] Hemoglobin is a heterotetramer consisting of four subunits (two α and two β).
However, structurally and functionally hemoglobin is described better as (αβ)2, so we call it a dimer of two αβ-protomers, that is, a diprotomer.