True about allosteric inhibition is-: (A) Substrates of an enzyme mediate allosteric inhibition, (B) Citrate and ATP inhibiting PFK-1 is a classical example, (C) The allosteric inhibitor directly binds to the active site of the enzyme, (D) It is only homotropic allosteric regulation
Answer is B. Ans. is 'b' i.e., Citrate and ATP inhibiting PFK-1 is a classical example* Allsoteric inhibition is mediated, when a regulator binds to a site, other than the catalytic site. This site is called as allosteric site, (alio means other than). Hence the allosteric regulator never binds to the active site of an enzyme.* This binding of regulator to allosteric site brings about a change in the conformation of the enzyme.* Asa result of change in conformation of the enzyme, affinity of the enzyme for the substrate in the active site is reduced.* It is a form of heterotropic allosteric regulation. Hence allosteric inhibition is not a form of homotropic allosteric regulation.* In homotropic allosteric regulation, the substrate acts as an allosteric regulator as well. Substrates always bring about allosteric stimulation, not inhibition.* Allsoteric inhibition is most commonly an exemplification of feed back inhibition or product inhibition.* Examples for allosteric inhibition are-# Citrate and ATP inhibiting Phosphofructokinase-1 (PFK-1)* PFK-1 is the rate limiting enzyme of glycolysis* ATP and citrate are products of glycolysis* Hence the products Citrate and ATP in a feed back mechanism mediate allosteric inhibition of PFK-1