Which of the following is physiological uncoupler-

Ans. is 'a' i.e.* Thermogenin o Amongst the given options, a, b and c are uncouplers.o However, only thermogenin, among these three is a natural (physiological) uncouplex.Uncoupleso 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 ATPQ by uncoupling the linkage between ETC and phosphorylation. Thus the energy instead of being trapped by phosphorylation is dissipated as heat. Uncouplers may beNatural:- Thermogenin, thyroxineSynthetic :- 2, 4-dinitrophenol (2, 4-DNP), 2, 4-dinitrocresol (2, 4-DNC), and CCCP (chlorocarbonylcyanidephenvl hvdrazone).o Thermogenin is an uncoupler protein present in brown adipose tissue (brown fat0). It uncouples oxidation and phosphorylation by acting as a channel for IT ions so that hydrogen ion gradient cannot build up. Oxidation occuring in brown adipose tissue without generation of ATP results in production of heatQ .