This document discusses different types of enzyme inhibition including reversible and irreversible inhibition. Reversible inhibition includes competitive, uncompetitive, non-competitive, mixed, partial, substrate and allosteric inhibition. Competitive inhibitors compete with the substrate for the active site, while uncompetitive inhibitors bind only to the enzyme-substrate complex. Non-competitive inhibitors bind at a site other than the active site. Irreversible inhibitors form covalent or non-covalent bonds that permanently inactivate the enzyme. Understanding inhibition is important as many drugs and toxins function through inhibiting enzymes.

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!
Contents

3. Introduction
•Enzymes are biomolecules that catalyse specefic reactions. They 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 enzymeslaboris 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 (CO2
-.CH2.CO2
-) 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

11. 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

12. 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

14. Fructose 1,6-bisphosphatase inhibition by AMP
● High ammounts of AMP signal that ATP levels are low
Pi

15. 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

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

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

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

21. Feedback inhibition of isoleucine synthesis in E. coli

22. 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

23. ● 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

25. Penicillin is irreversible inhibitor of transpeptidase

26. 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

27. ● 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

28. 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. 7th
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/che
m106/Supplemental/5 enzyme kinetics-inhibition