 Hemoglobin A

Hemoglobin A, commonly HbA, is the major adult human hemoglobin assembly made of two alpha-globin and two beta-globin chains, ${\alpha }_2{\beta }_2$.^[ref] It is one hemoglobin form rather than a name for every hemoglobin molecule present in an adult. Fetal hemoglobin has a different non-alpha-chain composition.

Human deoxyhemoglobin structure 4HHB is a primary structural example. The associated study refined the model at $1.74\mathring{\mathrm{A}}$ using room-temperature diffraction data recorded on film with a synchrotron X-ray source.^[ref] This connects the abstract ${\alpha }_2{\beta }_2$ notation with experimentally determined chain and haem organization.

Composition and oxygenation are independent descriptors. Hemoglobin A can occur in oxygenated or deoxygenated states while retaining its alpha/beta identity. Each intact tetramer contains four haem sites, so a concentration expressed per tetramer differs by a factor of four from a haem-equivalent concentration.

For an original accounting example, take a pure preparation at 1.00 g/L and use a stipulated nominal tetramer molar mass of $64,500\mathrm{g}\mathrm{mo}{\mathrm{l}}^{-1}$. Thenand haem-site concentration is about $62.02\mu \mathrm{mol}{\mathrm{L}}^{-1}$. If all sites are functional and mean oxygen occupancy is 0.80, bound oxygen concentration is about $49.61\mu \mathrm{mol}{\mathrm{L}}^{-1}$. Oxygen dissolved outside the protein is an additional pool. The assumptions are explicit teaching conditions, not a physiological reference range.

A primary spectral study measured both fetal and adult hemoglobin derivatives and found differences relevant to multicomponent analysis.^[ref] A measurement model should therefore state which protein-form and oxygenation-state spectra it uses, alongside the basis of the reported concentration.