Because it is associated with cooperative oxygen binding.

Because it is associated with cooperative oxygen binding. NONCOOPERATIVE VS. COOPERATIVE OXYGEN BINDING Noncooperative oxygen binding is commonly associated with myoglobin. It is a monomer. It has a hyperbolic oxygen binding curve and does NOT have cooperative oxygen binding. This is described as: ##Y_(O_2) = (P_(O_2))/(K_D + P_(O_2))## where ##Y## is the fractional saturation (y-axis) ##P_(O_2)## is the partial pressure of oxygen in ##torr## (x-axis) and ##K_D## is the dissociation constant for binding events. ##K_D## is smaller for higher binding affinities. Cooperative oxygen binding is basically an effect where oxygen binding affinity can change depending on how much oxygen is bound and this is described via a sigmoidal binding curve. HEMOGLOBIN Hemoglobin an ##alpha_2beta_2## heterotetramer is the prime example for sigmoidal oxygen binding curves. Its binding curve is defined as: ##Y_(O_2) = (P_(O_2)^n)/(P_50^n + P_(O_2)^n)## where ##Y## is the fractional saturation (y-axis) ##P_(O_2)## is the partial pressure of oxygen in ##torr## (x-axis) ##P_50## is the partial pressure of oxygen when ##K_D = P_(O_2)## and ##K_D## is the dissociation constant for binding events. ##n

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