myoglobin-keyproperties

myoglobin-keyproperties内容摘要：

)1 + ….] / ([Hb] + [ Hb(O2)1 + ….]) Hemoglobin O2 Binding Curve  Binding curve is sigmoidal  Artery: high pO2, loading of protein  Vein: lower pO2, unloading from protein  P50(hemoglobin) = 26 torr, adjusts as needed!! *Drastic change in pO2 over physiological range* Cooperativity in Binding O2 The sigmoidal shape is a consequence of the 4 subunits of hemoglobin cooperating in the binding of O2. • As pO2 increases and [O2] increases, increasing probability that at least 1 subunit has bound O2. Binding of O2 to a subunit INCREASES the probability that empty subunits will be able to bind an O2!! • As pO2 increases even further, the probability that remaining binding sites will have O2 bound increases. • Eventually, a plateau is reached: when most hemoglobins are filled there are few sites left to bind to, so not much increase, even if the pO2 is very high. The Hill Equation • Simplification is required to solve binding equation: assume O2 binding cooperativity is infinite • Binding curve can be expressed in terms of [O2]: YO2 = [O2]n / (Kd + [O2]n) • O2 is a gas: substitute pO2 for [O2] and use Kd = P50: YO2 = (pO2)n / (P50 + (pO2))n This expression for the degree of saturation of Hb is known as the Hill Equation • The quantity n is called the Hill Constant Interpretation of the Hill Equation YO2 = (pO2)n / (P50 + (pO2))n • n: the degree of cooperativity in ligand binding  n = 1: noncooperative  n 1: positive cooperativity implies binding of a ligand increases affinity for next ligand.  n 1: negative cooperativity implies binding of a ligand decreases affinity for next ligand. • Rearranging the Hill equation allows Hill Plots to be。