Which of the following is an effect of dinitrophenol on oxidative phosphorylation.
|A||Inhibition of cytochrome b|
|B||Blockade of both electron transport and ATP synthesis|
|C||Inhibition of ATP synthesis with normal electron transport|
|D||Inhibition of electron transport but not ATP synthesis.|
Fig.: Proposed sites of inhibition (-) of the respiratory chain by specific drugs, chemicals, and antibiotics. The sites that appear to support phosphorylation. BAL, dimercaprol. TTFA is an Fe-chelating agent. Complex, NADH: ubiquinone oxidoreductase; complex II, succinate: ubiquinone oxidoreductase; complex Ill, ubiquinol: ferri cytochrome c oxidoreductase; complex IV, ferr cytochrome C: oxygen oxidoreductase.
Respiratory chain and inhibition (Must read)
a. Component of the respiration chains are arranged in order of increasing Redox-potential.
b. H+ or electron (e) (Reducing equivalents) flow through the chain in steps form more electro negative
component to the more electro +ve through a redox potential 1.1 volt from NAD+/NADH to O2/2H2O.
c. ‘Q’ or Ubiquinone or, Co-enzyme Q — linking between flavoprotein and cyt. b. It is mobile; Q is
constituent of the mitochondrial lipid. Structure of the Q is similar to vit. K and vit E, and planto quinone (All characterized by Poly-iso-pyrenoid side chain.* cyt. c:- is only soluble cyt.)
d. One glucose, on complete combustion gives — 2870 KJ energy but only 68% of the energy is conserved or captured in the form of ATP.
NAD — dehydrogenase 3ATP, P: O ratio =2.5
Flavoprotein (FAD) — dehydrogenase = 2ATP, P:O ratio =1.5
e. Conditions limiting the rate of Respiration:
State 1 — Availability of ADP and substrate
State 2— Availability of substrate only
State 3 — The capacity of the respiratory chain itself when all substrates and components are present in saturating amounts.
State 4 — Availability of ADP only. (State 4 is most important, generally most cells in the resting state are instate 4, and respiration is controlled by the availability of ADP)
State 5 — Availability of O2 only.
6. Inhibitors of Respiratory chains : 3—types: -
a. Inhibitors of respiratory chain proper
b. Inhibitors of oxidative phosphorylation
c. UN couplers of oxidative phosphorylation.
a. Barbiturate (Amobarbital), Piecrcidin A and Rotenone (Insecticide and fish poisons): - they prevent oxidation of substrate that communicates directly with respiratory chain via — NAD-linked deHase by blocking the transfer from FeS to Q
b. Dimercaprol (BAL) and Antimycin A: - inhibit respiratory chain between cyt. b and cyt C
c. H2S, CO. CN- (cyanide): - inhibits cyt. Oxidase (cyt. aa3) and totally arrest the respiration.
d. Caboxin and TTFA: - inhibits transfer of ‘H+ or ‘e’ from succinate deHase to Q; whereas Malonate is a competitive inhibitor of succinate deHase
e. Oligomycin — block oxidation and phosphorylation
f. UN couplers → to dissociate oxidation in the Respiratory chain from phosphorylation.
Eg. Dinitrophenol: - Oxidation proceeds without phosphorylation i.e. electron transfer occurs
(oxidation) without ATP formation (phosphorylation)
• Dinitrocresol, penta chlorophenol and CCCP → inhibit in similar manner as dinitrophenol.
• CCCP (m-chloro carbonyl cyanide phenylhydrazone) is 100 times as active as dinitrophenol.
g. Atractyloside: - inhibits oxidative — phosphorylation, it is considered to inhibits the transport of ADP into the mitochondria and of ATP out of the membrane.
h. Malate shuttle: - for transfer of reducing equivalents (H+ or ‘e) from cytosol into mitochondria consists of keto glutarate transporters, glutamate-Aspartate transporter, malate de Hase and transaminase.
i. MELAS (Mitochondrial myopathy, encephalopathy Lactic acidosis, and seizures (- is an inherited condition due to NADH: Ubiquinone oxidoreductase (complex —P) or cyt. aa3 deficiency.