Which complex of electron transport chain is inhibited by cyanide?
Ans. is 'd' i.e., Complex IV* Cyanide inhibits the electron transport from complex IV to oxygen* Inhibitors of respiratory chain may be divided into three groups : -1) Inhibitors of electron transport chain proper# These inhibitors inhibit the flow of electrons through the respiratory chain. This occurs at following sites.i) Complex I (NADH to CoQ) is inhibited by: - Barbiturates (amobarbital), Piericidin A (an antibiotic), rotenone (an insectiside), chlorpromazine (a tranquilizer), andguanethidine (an antihypertensive). These inhibitors block the transfer of reducing equivalents from FeS protein to CoQ.ii) Complex II is inhibited by; - Carboxin and TTFA inhibit transfer of electon from FADH2 to CoQ, whereas malanate competitively inhibit from succinate to complex II.iii) Complex III (Cytochrome b to cytochrome Cl) is inhibited by; - Dimercaprol antimycin A, BAL (British antilewisite), Naphthyloquinone. These inhibitors block the transfer of electrons from cytochrome b to cytochrome C1iv) Complex IV (cytochrome C oxidase) is inhibited by: - Carbon monoxide, CN-, H2S and azide (N3). These inhibitors block the transfer of electrons from cytochrome aa3 to molecular oxygen and therefore can totally arrest cellular respiration.2) nhibitors of oxidative phosphorylation# These compounds directly inhibit phosphorylation of ADP to ATP.# Oligomycin inhibits F0 component of F0F1 ATPase.# Atractiloside inhibits translocase, a transport protein that transports ADP into mitochondria for phosphorylation into ATP.3) Uncouples# As the name suggests, these componds block the coupeling of oxidation with phosphorylation. These compounds allow the transfer of reducing equivalents in respiratory chain but prevent the phosphorylation of ADP to ATP by uncoupling the linkage between ETC and phosphorylation. Thus the energy instead of being trapped by phosphorylation is dissipated as heat.# Uncouplers may bei) NaturalThermogenin, thyroxineii) Synthetic 2, 4-dinitrophenol (2, 4-DNP), 2, 4-dinitrocresol (2, 4-DNC), and CCCP (chlorocarbonylcyanidephenyl hydrazone).
Complex I
Complex II
Complex III
Complex IV
Respiratory Chain