myoglobin-keyproperties(存儲版)
【正文】 2] = 1 …… [Mb] = [MbO 2] Myoglobin O2 Binding Properties Mb + O2 ? MbO2, Kd = [Mb] [O2] / [MbO2] ? To think about O2 transport, express binding in terms of the fraction of occupied binding sites, . Fractional Saturation (YO2): YO2 = [MbO2] / ([Mb] + [MbO2]) ? Substituting with Kd, allows understanding of transport properties in terms of O2 availability: YO2 = [O2] / (Kd + [O2]) Myoglobin O2 Binding Properties YO2 = [O2] / (Kd + [O2]) ? O2 is a gas: express [O2] as partial pressure (pO2) [Common to call pO2 oxygen tension] YO2 = pO2 / (Kd + pO2) ? As pO2 increases, binding increases ? Binding curve is hyperbolic, not linear (just like enzymes!!!) [Draw] ? Low pO2 ? little binding to protein ? High pO2 ? saturation of protein ? At halfsaturation pO2 = Kd, field uses term P50 ? P50(myoglobin) = torr / pO2 = 10100 torr invivo!! Hemoglobin Key Properties ? Ubiquitous O2 transport protein ? A globular soluble protein, 2X2 chains (164 kDa) ? a and b chains 44% identical ? All helical secondary structure (like myoglobin) ? abab quaternary structure ? asubunit 141 residues ? bsubunit 146 residues ? Extensive contacts between subunits ? Mix of hydrophobic, Hbond, and ionic interactions ? a1b1 (a2b2) 35 residues, a1b2 (a2b1) 19 residues Structure of Hemoglobin Intersubunit contacts b2 Heme b1 a2 a1 Hemoglobin O2 Binding Properties Hb + nO2 ? Hb(O2)1 + Hb(O2)2 + Hb(O2)3 + Hb(O2)4 Kd = [Hb] [O2]n / [Hb(O2)1 + Hb(O2)2 + Hb(O2)3 + Hb(O2)4] [How’s that for plicated!?!?!] ? To think about O2 transport, express binding in terms of the fraction of occupied binding sites, . Fractional Saturation (YO2): YO2 = [Hb(O2
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