OXIDATION PHOSPHORYLATION-1 BIOC DR. TISCHLER LECTURE 28

OBJECTIVES 1.Reduction potential differences (  E o ); general relationship between  E o and the free energy difference  G o 2.Essential features of oxidative phosphorylation and the role of redox reactions in the e - transport (respiratory) chain 3.For the respiratory chain major complexes (I to IV): a) identify by name b) components that donate electrons to and accept electrons c) prosthetic groups important in the electron transfer; d) explain how energy from complexes is conserved and which ones produce sufficient energy to make ATP.

REDUCTION-OXIDATION REACTIONS Oxidative portion of oxidative phosphorylation: redox reactions Phosphorylation portion is ADP + P i  ATP Two half reactions: Reductant 1  Oxidant 1 + e - Oxidant 2 + e-  Reductant 2 Overall reaction: Reductant 1 + Oxidant 2  Reductant 2 + Oxidant 1 Redox reactions are exergonic because  G o is negative:  G o = -nF  E o

H+H+ outer membrane intermembrane space inner membrane matrix e-e- O2O2 H2OH2O ADP+ Pi ATP Figure 1. Essential features of oxidative phosphorylation. redox reactions of respiratory chain use electrons to reduce oxygen to water energy generated moves protons from matrix to intermembrane space inward movement of protons recovers this energy to promote formation of ATP in the matrix. H+H+

Figure 2. Overview of the respiratory chain showing the progression of reduction potentials from strong to weak reductants culminating in oxygen as the ultimate electron acceptor. The  E o values are the potential differences across the four complexes electron flow  E o ' = 0.42V I NADH Coenzyme Q E o ' = -0.32VE o ' = 0.10V  E o ' = 0.19V III Cytochrome C E o ' = 0.29V  E o ' = 0.53V IV ½ O 2 E o ' = 0.82V  E o ' = 0.07V E o ' = 0.03V II Succinate

Table 1. Summary of the redox complexes of the electron transport chain Complex designation Prosthetic groupsFunction I - NADH-Q reductase FMN (flavin mono- nucleotide); Fe-S oxidizes NADH to NAD + ; transfers e - to coenzyme Q II – Succinate-Q reductase FAD; Fe-Soxidize succinate to fumarate; reduction of FAD to FADH 2 ; e - transfer to CoQ III - Cytochrome reductase heme b; heme c 1 ; Fe-S transfers e - between CoQ and cytochrome C (reduced) IV - Cytochrome C oxidase heme a; heme a 3 ; Cu oxidizes cytochrome C; reduces ½O 2 to H 2 O

Figure 3. Complex I of the respiratory chain that links NADH and coenzyme Q. DH is NADH dehydrogenase. NADH NAD + NADH DH CoQ Complex I: NADH-Q reductase Prosthetic groups: FMN; Fe-S

Figure 4. Complex II of the respiratory chain. SDH is succinic dehydrogenase an enzyme of the citric acid cycle. FAD FADH 2 Succinate Fumarate SDH Complex II: Succinate-CoQ reductase Prosthetic groups: FAD; Fe-S CoQ

Figure 5. Complex III of the respiratory chain linking CoQ and cytochrome C. CoQ cyt b/cyt c 1 Complex III: cytochrome reductase Prosthetic groups: heme b; heme c 1 ; Fe-S cyt c Electrons from complex I or II

Figure 6. Complexes III and IV linked by cytochrome C with complex IV reducing oxygen to water. cyt b/cyt c 1 cyt c cyt a-a 3 ½ O H + H2OH2O Complex III Complex IV: Cytochrome C oxidase Prosthetic groups: heme a; heme a 3 ; Cu