sentences:  In chemistry, a so-called protomer is a molecule which displays tautomerism due to position of a proton.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.