myoglobin-keyproperties(編輯修改稿)
2024-11-29 17:26 本頁面
【文章內(nèi)容簡介】 )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
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