L19_hb2_462a_2013

# Tave descripon of degree of cooperavity hill equaon

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Unformatted text preview: R state and the T state. •  Explain how CO2 binds to Hb in the .ssues, its eﬀect on O2 binding, and why it is released in the lungs. •  Explain how H+ binding and CO2 binding relate to the transport func.ons of Hb (binding and release of the various ligands in the lungs and in the .ssues). The Hill Equa;on •  Archibald Hill (1913) •  Quan.ta.ve descrip.on of degree of coopera;vity •  Hill Equa;on (binding of n molecules of O2 to Hb): rearrange θ pO2n = 1 ­ θ P50n Taking log of both sides gives linear form of Hill Equa;on: Hill equa*on The Hill Plot Hill coeﬃcient, nH, deﬁned as: nH = slope where log { θ/(1–θ) } = 0 i.e., where θ = 0.5, θ = 1 – θ Hill plot for Mb: line w/nH=1 Hill plot for Hb: 3 parts of plot: 1)  low pO2 2)  high pO2 3)  intermediate pO2 Hb: nH ≈ 3 (depends on condi.ons) Hill plot Interpreta;on of the Hill Coeﬃcient •  nH = 1: no coopera*vity –  either just 1 binding site per protein (e.g., Mb), or if mul.ple sites, they don’t communicate. –  A standard plot of θ vs. [ligand] will have a hyperbolic binding curve •  nH &lt; 1: nega*ve coopera*vity (“compe**ve binding”) –  Binding of ligand to one site reduces aﬃnity for other sites (rare) •  nH &gt; 1: posi*ve coopera*vity (“coopera*ve binding”) –  A standard plot of θ vs. [ligand] will have a sigmoid binding curve •  Maximal possible value of nH = number of binding sites (= number of subunits, for Hb, i.e., 4) –  Hill coeﬃcient always &lt; max. value –  If nH = number of subunits, that’s max. possible posi.ve coopera.vity: no par.ally saturated protein m...
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## This test prep was uploaded on 02/25/2014 for the course BIOC 462A taught by Professor Ziegler,baldwin during the Spring '08 term at University of Arizona- Tucson.

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