TheRoot effect is a physiological phenomenon that occurs infishhemoglobin, named after its discoverer R. W. Root. It is the phenomenon where an increasedproton orcarbon dioxide concentration (lowerpH) lowers hemoglobin's affinity and carrying capacity foroxygen.[1][2] The Root effect is to be distinguished from theBohr effect where only the affinity to oxygen is reduced. Hemoglobins showing the Root effect show a loss of cooperativity at low pH. This results in theHb-O2 dissociation curve being shifted downward and not just to the right. At low pH, hemoglobins showing the Root effect don't become fully oxygenated even at oxygen tensions up to 20kPa.[2] This effect allows hemoglobin in fish withswim bladders to unload oxygen into the swim bladder against a high oxygen gradient.[3] The effect is also noted in the choroidrete, the network ofblood vessels which carries oxygen to theretina.[3] In the absence of the Root effect,retia will result in the diffusion of some oxygen directly from the arterial blood to the venous blood, making such systems less effective for the concentration of oxygen.[4] It has also been hypothesized that the loss of affinity is used to provide more oxygen to red muscle during acidotic stress.[5]
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