Myoglobine <> hémoglobine α2β2 α 141 aas Β 146 aas α 153 aas 18 % d’identité
8 (α loop α) (A>H) Domaine globine hydrophobe
Structure Tétrapyrrolique
Protoporphyrine IX Fe: 6 orbitales D His O2---His Fixation de O2 = oxygenation
Groupement acide propionique
Indépendance des 4 hèmes
O 2 Gaz hydrophobe>> peu soluble Mb et Hb servent de transporteurs
Fraction sites occupés/ Sites totaux
Pourquoi structure quaternaire ???? Hb acquiert des propriétés plus complexe que la myoglobine - son affinité est adapté à l’état de l’environement (interaction de molécules) Proton (effet Bohr) 2,3 BPG
carbaminohemoglobine Anhydrase carbonique
Transport du CO2 -Transport isohydrique (70-80%) HCO3 - (anhydrase carbonique) -Transport par l’hemoglobine carbamino-hemoglobine -HbNH2 +CO2>>>>>HBNHCO2- + H+
Protéines allostériques Coopérativité dans l’interaction de l’oxygène
Figure 5.2 Champe et al, 3 rd edn Substrate binds to enzyme’s active site, where it is converted to product. glucose Hexokinase crystal structure note relative size of enzyme and substrate Note how structure changes on substrate binding
What an enzyme does E + S ESEPE + P The enzyme (E) binds substrate (S) and converts it to product (P). Note that E recycles. Overall, S P
Rate of an enzymatic reaction as a function of temperature and pH
Km – a measure of E-S affinity Km = [E].[S] [ES] When E is ½ saturated with S (v o = ½ V max ) Then [ES] = [E] and Km = [S] Units are M (mol/l) Km is the substrate concentration at which v o = ½ V max. low Km = high affinity high Km = low affinity