Complex-I in electron transpo chain is

ETC Complex-I i. It is also called NADH-CoQ reductase or NADH dehydrogenase complex. It is tightly bound to the inner membrane of mitochondria. ii. It contains a flavoprotein (Fp), consisting of FMN as prosthetic group and an iron-sulfur protein (Fe-S). NADH is the donor of electrons, FMN accepts them and gets reduced to FMNH2 (Fig.19.8). Two electrons and one hydrogen ion are transferred from NADH to the flavin prosthetic group of the enzyme. NADH + H+ + FMN - FMNH2 Summary of Electron Flow in ETC Complex I: NADH NADH NADH -- - FMN FMN FMN - Complex II: Succinate Succinate Succinate - -- Fe-S Fe-S Fe-S - -- CoQ -- FAD FAD FAD - -- Fe-S Complex III: CoQ CoQ CoQ - -- Fe-S Fe-S Fe-S - Fe-S Fe-S - -- cyt.b cyt.b cyt.b - CoQ CoQ - - - -- CoQ CoQ CoQ - - - -- cyt.c1 cyt.c1 cyt.c1 - - - cyt. c Complex IV: Cyt. c Cyt. c Cyt. c - -- cyt a-a3 cyt a-a3 cyt a-a3 - -- O O O222 cyt. c cyt. c iii. The electrons from FMNH2 are then transferred to Fe-S. The electrons are then transferred to coenzyme Q (ubiquinone) (CoQ). iv. The overall function of this complex is to collect the pair of electrons from NADH and pass them to CoQ. The reactions are shown in Fig. 19.8. v. There is a large negative free energy change; the energy released is 12 kcal/mol. This is utilized to drive 4 protons out of the mitochondriaRef: DM Vasudevan Textbook of Medical Biochemistry, 6th edition, page no: 228