The biophysical study of proteins has allowed an improved understanding of the relationship between form and function. This relationship is the basis of allostery, the modulation of protein function by association of allosteric effectors that cause conformational changes. The oxygen transporter hemoglobin (Hb) has been extensively studied since the 1960s. The functionality of Hb is naturally regulated by association of endogenously produced effectors such as 2,3-diphosphoglycerate (DPG). Quantification of effector binding strengths to Hb are useful for the development and comparison of compounds. Here, photoacoustic calorimetry (PAC) was employed in a novel way to quantify the dissociation constants (KD) and thermodynamic profiles of two known Hb effectors, inositol hexakisphosphate (IHP) and 8-hydroxypyrene-1,3,6-trisulfonic acid (pyranine) binding to oxygenated Hb (oxyHb). The KD values for IHP and pyranine were calculated at various temperatures and are consistent with previous studies. Environmental factors can also contribute to changes in protein shape. Perfluoroalkyl surfactants are a class of industrial compounds which have been studied recently due to their toxic properties and widespread contamination in foodstuffs and water sources. However, the effect of surfactants on protein structure is not well defined. Here, the effects of perfluorooctanoic acid (PFOA), a member of the perfluoroalkyl surfactant family, were examined on Hb structure using emission spectroscopy, transient absorbance, and circular dichroism spectroscopy. It was found that PFOA had a substantial effect on Hb conformation as evidenced by blue-shifting of the emission spectra, differences in affinity of Hb for carbon monoxide (CO), and changes in Hb secondary structure.
