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Unformatted text preview: PROTEIN FUNCTION I Ligand Binding 1 RECAP y = x x + C P + L PL K a = PL [ ] P [ ] L [ ] = fraction of total binding sites occupied = L [ ] L [ ] + 1 K a P + L PL = L [ ] L [ ] + K d 2 3 = O 2 [ ] O 2 [ ] + K d = O 2 [ ] O 2 [ ] + O 2 [ ] 0.5 = pO 2 pO 2 + P 50 O 2 is a gas. More appropriate to express concentrations of gas as pO 2 4 5 EFFECT OF GLOBIN ON O 2 BINDING BY HEME CO binds heme 20,000 times more tightly than O 2 to free heme K d for CO is 20,000 times smaller than K d for O 2 CO binds heme 200 times more tightly than O 2 to heme in myoglobin K d for CO is 200 times smaller than K d for O 2 6 EFFECT OF GLOBIN ON O 2 BINDING BY HEME partially explained by steric hindrance preferred mode of ligand binding by free heme mode of oxygen binding by heme in myoglobin 7 His 64 is referred to as the distal His and does not coordinate to the iron atom, but does interact with the axial ligand (O 2 ) His 93 is the proximal His and does coordinated to the iron but does not interact with O 2 E FFECT OF G LOBIN ON O 2 BINDING BY H EME His 64 His 93 8 His...
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- Fall '11