QUESTIONS :

1) Explain the working mechanisms of competitive inhibitor and non-competitive inhibitor.

In competitive inhibition, at any given moment, the enzyme may be bound to the inhibitor, the substrate, or neither, but it cannot bind both at the same time. In virtually every case, competitive inhibitors bind in the same binding siteas the substrate, but same-site binding is not a requirement. A competitive inhibitor could bind to anallosteric site of the free enzyme and prevent substrate binding, as long as it does not bind to the allosteric site when the substrate is bound. For example,strychnineacts as an allosteric inhibitor of the glycine receptor in the mammalian spinal cord and brain stem. Glycine is a major post-synaptic inhibitory neurotransmitter with a specific receptor site. Strychnine binds to an alternate site that reduces the affinity of the glycine receptor for glycine, resulting in convulsions due to lessened inhibition by the glycine. In competitive inhibition, the maximum velocity () of the reaction is unchanged, while the apparent affinity of the substrate to the binding site is decreased (thedissociation constant is apparently increased). The change in(Michaelis-Mentenconstant) is parallel to the alteration in. Any given competitive inhibitor concentration can be overcome by increasing the substrate concentration in which case the substrate will outcompete the inhibitor in binding to the enzyme. Non-competitive inhibition models a system where the inhibitor and the substrate may both be bound to the enzyme at any given time. When both the substrate and the inhibitor are bound, the enzyme-substrate-inhibitor complex cannot form product and can only be converted back to the enzyme-substrate complex or the enzyme-inhibitor complex. Non-competitive inhibition is distinguished from general mixed inhibition in that the inhibitor has an equal affinity for the enzyme and the enzyme-substrate complex. The most common mechanism of non-competitive inhibition involves reversible binding of the inhibitor to anallosteric site, but it is possible for the inhibitor to operate via other means including direct binding to the active site. It differs from competitive inhibition in that the binding of the inhibitor does not prevent binding of substrate, and vice versa, it simply prevents product formation for a limited time. This type of inhibition reduces themaximum rateof achemical reactionwithout changing the apparent bindingaffinityof thecatalystfor thesubstrate.

REFERENCES :

1) Wikipedia, non-competitive inhibition, 2 september 2014. http://en.wikipedia.org/wiki/Non-competitive_inhibition#Mechanism2) Chempages netorials, competitive inhibition. https://www.chem.wisc.edu/deptfiles/genchem/netorial/modules/biomolecules/modules/enzymes/enzyme5.htm 3) Differentiate between allosteric, non-competitive and competitive inhibition. 25 september 2013. http://www.researchgate.net/post/How_will_we_differentiate_between_allosteric_Non-competitive_and_uncompetitive_inhibition