1. Enzymes are proteins that accelerate biochemical reactions without being altered. They have high substrate specificity and increase reaction rates by lowering activation energy. 2. The active site of an enzyme is complementary to its substrate. Substrate binding occurs through lock-and-key or induced-fit models. 3. The rate of enzyme reactions is affected by substrate and enzyme concentration, temperature, and pH. Higher concentrations and temperatures increase rates while deviating from optimal pH decreases rates.

1. SPS505 Exercise Biochemistry

2. Learning outcomes
At the end of the lesson, students should be able to
1. Define the function of enzymes
2. Explain the mechanisms of enzyme action
3. Describe the substrate recognition models
4. Describe how enzyme affects the rate of reaction

3. Enzymes
• One of the most important functions of proteins is to act as
enzymes
• Enzymes are biological substances that accelerate biochemical
reactions without being altered in the end
• They are usually named after their substrate or the kind of
reaction they catalysed
• Most enzyme names end in “ase” (e.g. ATPase, lipase, amylase)
• The reactants in an enzyme reaction are called the substrates
S P
E
Enzyme reaction
• The conversion of substrate (S) to
product (P) with the aid of an
enzyme (E) can be symbolized as
follows

4. Enzymes
• 3 main features
1. Enzymes have high specificity
1. Each enzyme catalyzes specific reactions and
recognize only specific substances as substrate
2. Enzymes increase the rate of reaction (by 100 million-10
billion times quicker)
• In the absence of enzymes, most reactions in living
organisms would be too slow to support life
3. The rate of reaction is affected by several factors
• Substrate concentration
• Enzyme concentration
• Temperature
• pH

5. The Active Site
5
• The specificity of an enzyme is due to the complementary
structure of the active site to the substrate
• Active site is a small area on the surface of the enzyme that
attracts the substrates(s) and facilitates product formation

6. Substrate Recognition
6
Lock-and-key model
 substrate fits exactly into active site like a key fits the proper lock
Induced-fit model
 active site is not complementary to the substrate but their
interaction modifies the shape of both resulting in an accurate fit

7. Enzyme Affects the Rate of a Reaction
7
• When chemical reaction occurs in a system (e.g. cell), the
energy of the system usually changes because the products
have a different energy level from that of the reactant
• It is impossible to measure the absolute values of energy,
only the change in free energy (ΔG) can be measured
Exergonic reaction (ΔG < 0)
• energy-producing reaction
• can occur spontaneously
• do not require additional energy
Endergonic reaction (ΔG > 0)
• energy-consuming reaction
• non-spontaneous
• require additional energy from
an external source

8. Enzyme Affects the Rate of a Reaction
8
• Enzyme affects the rate of a reaction but they do not
determine the direction of reaction
• This is because the rate of reaction is not connected to ΔG
but relates to the transition state
Activation energy (∆G‡)
• The energy input required to start the reaction
• The higher the activation energy value, the more difficult
the activation of the substrate is
• The slower the reaction will go

9. 1. When enzyme binds the substrate at their active sites, enzyme
• lowers the activation energy
• speeds up the formation of the transition state
• increases the rate of reaction
2. Because enzyme do not affect the value of ΔG, they do not
determine the direction of reaction
1
2

10. INDICATE IN THE IMAGE BELOW
HOW ENZYMES INCREASE THE
RATE OF REACTION

11. Factors that affect the rate of enzyme reactions
1. Substrate concentration
• ↑ substrate concentration ↑ reaction rate
• More substrates are binding to the enzyme
• When all active sites are occupied by substrate, further
increase in substrate concentration will have no effect on
the reaction rate

12. Factors that affect the rate of enzyme reactions
2. Enzyme concentration
• ↑ enzyme concentration ↑ reaction rate
• There will be more active sites available for substrate
binding
• Endurance training adaptation rely on the cell’s ability to
adjust enzyme concentration to increase reaction rate
• Cells response to endurance training by making new
proteins to increase enzyme concentration and metabolic
reaction rate

13. Factors that affect the rate of enzyme reactions
3. Temperature
• ↑ temperature ↑ reaction rate
• Temperature increases the kinetic energy of molecules &
increase the percentage of effective collision
• Temperature above 50°C will lead to denaturation where
enzyme activity is decreased or lost

14. Factors that affect the rate of enzyme reactions
4. pH
• Different enzyme have different optimum pH at which they
achieve their maximum rate of reaction
• As pH ↑ or ↓ from the optimum level, the reac?on rate ↓ due
to changes in the structure of the active site
• Enzymes in our muscle usually function optimally ~7
• During high-intensity exercise, pH can range from 7.1 to 6.6
• Therefore, acidosis-induced inhibition of metabolic enzyme is
linked to fatigue during high-intensity exercise
Active site
Optimum pH High or low pH

15. WHAT ARE THE FACTORS THAT AFFECT
THE RATE OF ENZYME REACTIONS?

16. Glucose-6-phosphatase (G6P) Deficiency
• Deficiency of this enzyme causes glycogen storage disease
(accumulation of glycogen in organs especially liver
resulting in hepatomegaly)
• Main metabolic effects of G6P deficiency:
• Inability to maintain blood glucose level during post-
absorptive hours (hypoglycaemia)
• Lactic acidosis, hypertriglyceridemia, hyperuricemia
• G6P is needed to hydrolyse
glucose-6-phosphate (from
gluconeogenesis &
glycogenolysis) into glucose and
inorganic phosphate

17. Glucose-6-phosphate Dehydrogenase
(G6PD) Deficiency
• G6PD is needed to produce NADPH and
glutathione (an important antioxidant
in the body)
• Red blood cells are especially sensitive
to oxidative damage
• Oxidative stress due to
certain medications
(antimalarial drugs &
sulphonamides), foods (fava
beans) and infections (URTI
& GI infections) can cause
acute haemolytic anaemia

18. References
• MacLaren, D., & Morton, J. (2011). Biochemistry for
sport and exercise metabolism. John Wiley & Sons.
• Campbell, M., & Farrell, S. (2007). Biochemistry:
Cengage Learning.
• Mougios, V. (2006). Exercise Biochemistry: Human
Kinetics.
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