Enzyme Inhibition

Reversible and irreversible inhibition with kinetics
Introduction
Competitive inhibition
Non competitive inhibition
Uncompetitive inhibition
Mixed inhibition
Substrate inhibition
Feedback inhibition
Irreversible inhibition

1. Enzyme Inhibition Darshan

2. Found around the house! Introduction Reversible inhibition (Competitive, uncompetitive, non- competitive, mixed, partial, substrate and allosteric inhibition) Irreversible inhibition Conclusion Reference Found around the house! Cont ents

3. Introduction Enzymes are biomolecules that catalyse specefic reactions. T hey enhance the rate of the reaction by providing a reaction pathway with a lower activation energy Active site : region of an enzyme surface that binds the substrate molecule and catalytically transforms it to product Inhibitors : substances which tend to decrease the rate of an enzyme-catalysed reaction Inhibiting enzyme activity serves as a major control mechanism in biological systems Many drugs and toxic agents act by inhibiting enzymes laboris nis

4. Kinetics

5. Reversible inhibition Bind to an enzyme in a reversible manner Can be removed by dialysis (or simple dilution) Competitive inhibition Uncompetitive inhibition Non-competitive inhibition Mixed inhibition Partial inhibition Substrate inhibition Allosteric inhibition

6. Competitive Inhibition     Inhibitors are structurally similar to substrate Inhibitors and substrate compete for common active site Enzyme-bound inhibitor either lacks the appropriate reactive group or it is held in an unsuitable position with respect to the active site

7. The effect of competitive inhibitor depends on the inhibitor concentration, the substrate concentration and relative affinities of the substrate and the inhibitor for the enzyme

8. Malonate (CO 2 - .CH 2 .CO 2 - ) is a competitive inhibitor of the reaction catalysed by succinate dehydrogenase Similarity: two carboxyl groups Limiting factor: malonate unlike succinate, has only one carbon atom between carboxyl groups Hence subsequent reaction involving formation of double bond cannot take place

9. Uncompetitive inhibition Inhibitors bind only to enzyme-substrate complex and not to free enzyme Substrate binding could cause a conformational change to take place Inhibitor does not compete with the substrate for the same binding site

10. Alkaline phosphatase inhibition by phenylalanine At alkaline pH alkaline phosphatase catalyses the release of inorganic phosphate from phospha -te esters L-phenylalanine prevents dephosphoryla -tion after binding to enzyme-substrate complex

11. Non-competitive inhibition Inhibitor can combine with an enzyme molecule to produce a dead end complex, regardless of whether a substrate molecule is bound or not

12. Fructose 1,6-bisphosphatase inhibition by AMP High ammounts of AMP signal that ATP levels are low P i

13. Mixed inhibition In non-competitive inhibitor constant for both EI and ESI complex are same The term mixed inhibition is based on the concept that there are different inhibitor constants for the following processes

14. Partial inhibition Enzyme-inhibitor complexes are not dead ones The possible breakdown of ESI complex to yield products

15. Substrate inhibition Substrates in very high concentrations can inhibit it’s own conversion into product

16. Allosteric inhibition Animation link: https://youtu.be/X9nQ6Qx16GM

17. Feedback inhibition of isoleucine synthesis in E. coli

18. Irreversible inhibition An irreversible inhibitor dissociates slowly from its target enzyme because it has strong association with enzyme, either covalently or non-covalently. Inhibitor-enzyme interaction is irreversible

19. Inhibitor possess great affinity for the enzyme Inhibition is progressive Inhibitor permanently inactivates the enzyme The net effect is to remove enzyme from the reaction

20. Penicillin is irreversible inhibitor of transpeptidase

21. Conclusion Inhibitors decrease the rate of an enzyme catalysed reactinon Competitive inhibitors compete for same active site. They change Km (increase) Uncompetitive inhibitors bind to ES complex. Altering both Km and Vmax Non-competitive inhibitors bind to site other than substrate binding site on the enzyme, regardless substrate has bound to enzyme or not. Km is unchanged, Vmax is decreased High substrate concentrations may lead to inhibition

22. In allosteric inhibition excess downstream products bind to allosteric site of enzymes of primary steps and cause conformational changes in active site Irreversible inhibitors tightly bind to target enzymes usually by covalent bonds and permanently inactivates the enzymes. The reaction cannot attain maximum velocity

23. Reference Trevor Palmer, 2004. Enzymes: Biochemistry, Biotechnology, Clinical Chemistry. East-West Press Pvt Ltd. New Delhi: 107-117, 128-149 Jeremy M. Berg, John L. Tymoczko, Lubert Stryer, 2012. Biochemistry. 7 th edition. W. H. Freeman and Company New York: 238-240 David L. Nelson, Michael M. Cox, 2013. Lehninger Principles of Biochemistry. Sixth edition. W. H. Freeman and Company New York: 28-29 http://bohr.winthrop.edu/faculty/hurlbert/link_to_webpages/courses/chem106/Supplemental/5 enzyme kinetics-inhibition

24. Thank you!