1. Factors Influencing Enzyme Action
Substrate
Active site
Enzyme
Enzyme-substrate
complex
Substrate
Active site
Enzyme
Enzyme-substrate
complex

2. Enzyme reactions enzyme + substrate enzyme + products
enzyme-substrate complex
enzyme + products

3. Factors that affect enzyme rates of reaction
An enzyme’s rate of reaction is measured by the amount of substrate converted to a product per minute.
An enzyme’s activity can be affected by:
General environmental factors, such as temperature and pH.
Cofactors and coenzymes.
Enzyme and substrate concentration which affects the saturation of the active site.
Inhibitors.

4. What is the effect of temperature on enzyme function?
Optimal temperature for
typical human enzyme
enzyme of thermophilic
(heat-tolerant
bacteria)
Temperature (°C)
Optimal temperature for two enzymes 20 40 60 80
100
Rate of reaction
Optimal pH for pepsin
(stomach enzyme)
Optimal pH
for trypsin
(intestinal
enzyme) pH
Optimal pH for two enzymes 1 2 3 4 5 6 7 8 9 10
What is the effect of temperature on enzyme function?
What is the effect of pH on enzyme function?

5. 1. Environmental Factors
Each enzyme has an optimal temperature in which it can function.
Each enzyme has an optimal pH in which it can function.
The wrong temperature of pH can denature an enzyme, which means the enzyme proteins shape is destroyed.

6. 2. Cofactors and Coenzymes
Cofactors are nonprotein inorganic enzyme helpers.
For example, metal ions like iron in hemoglobin hold oxygen.
Coenzymes are organic cofactors.
For example, vitamins like niacin which serves as an electron acceptor.

7. Example of Cofactor Enzyme Activation: Binding of one oxygen to hemoglobin activates other sites to enhance oxygen binding at the three other sites. 7

8. 3a. Enzyme Concentration
What does the graph tell us about the effect of increasing [enzyme]?
Rate of Reaction
Enzyme Concentration
Increasing the [enzyme] means the rate of reaction keeps increasing.

9. 3b. Substrate Concentration
What does the graph show us about [substrate]?
Increasing [substrate] only increases the reaction rate until all the enzyme active sites are in use.

10. 4. Enzyme Inhibitors
Competitive inhibitors bind to the active site of an enzyme, competing with the substrate.
Noncompetitive inhibitors bind to another part of an enzyme, causing the enzyme to change shape and making the active site less effective.
Noncompetitive inhibition is also called allosteric regulation.

11. LE 8-19 A substrate can normally bind to the active site of an enzyme.
Normal binding
A competitive Inhibitor
mimics the substrate,
competing for the active site.
Competitive
inhibitor
Competitive inhibition
A noncompetitive inhibitor binds
to the enzyme away from the
active site, altering the shape
of the enzyme so that its
active site no longer functions.
Noncompetitive inhibitor
Noncompetitive inhibition

12. AZT and AIDS
AZT is the first retroviral drug approved to fight the HIV virus.
It is a competitive inhibitor for the enzyme reverse transcriptase. 12

13. Allosteric Regulation of Enzymes
Allosteric regulation is the term used to describe cases where an enzyme’s function is affected by the binding of a regulatory molecule at a different site than the active site.
Allosteric regulation may either inhibit or stimulate an enzyme’s activity.
Usually the end product of a long series of reactions that make a metabolic pathway inhibits an enzyme near the beginning of the pathway.
This way when the [product] is high the chemical reactions leading to the product are slowed down.

14. Allosteric Regulation

15. Homework Read MHR p 41 – 50 Do p 54 # 1 – 11, 13
Adapt and redraw the diagram on p43 to illustrate an anabolic reaction instead of a catabolic reaction.
Note: anabolic = synthesis catabolic = hydrolysis or breakdown

17. Feedback Inhibition Initial substrate (threonine) Active site
available
Threonine
in active site
Enzyme 1
(threonine
deaminase)
Isoleucine
used up by
cell
Intermediate A
Feedback
inhibition
Enzyme 2
Active site of
enzyme 1 can’t
bind
theonine
pathway off
Intermediate B
Enzyme 3
Intermediate C
Isoleucine
binds to
allosteric
site
Enzyme 4
Intermediate D
Enzyme 5
End product
(isoleucine) 17

18. Induced Fit Model of Enzyme Action
Substrates
Enzyme
Products
Substrates enter active site; enzyme
changes shape so its active site
Holds the substrates (induced fit).
Substrates held in
active site by weak
interactions, such as
hydrogen bonds and
ionic bonds.
Active site acts on substrates
Substrates are
converted into
products.
Products are
released.
Active
site is
available
for two new
substrate
molecules.
Quick Review of
Induced Fit Model of Enzyme Action
Enzyme-substrate
complex