1. Enzyme -3. Factors affecting enzyme activity Lecture NO: 1st MBBS
Dr Muhammad Ramzan

2. Enzyme activity - the definition
Enzyme activity refers to the catalytic ability of an enzyme
to increase the rate of a chemical reaction.
Turnover No: is the maximum number of molecules of substrate that an enzyme :
Can convert to products per catalytic site per unit time- mint.

3. Michaelis-Menten equation
 It is a set of mathematical expressions to calculate enzyme activity in terms of speed of reaction from measurable laboratory data.

4. Michaelis Menten equation

5. Conclusion of the equation
Characteristic of Km: It reflects the affinity of the E with S
Is equal to the Conc. of S at which reaction velocity is equal to ½ Vmax.Km does not vary with the conc. Of E
It is important in competitive inhibition when ↑ in S reverses the Vmax as inhibitor is diluted
Vmax: is achieved when all the active sites of E are occupied by the S
Vmax: Cannot be achieved in Non completive inhibition as inhibitor binds either to E or ES Complex.
↑in S has no effect as it cannot bind to active site

6. Measurement of Enzyme activity – Enzyme assay Carbonic Anhydrase – 36million.S/mint
Enzymes assays, measure the enzyme activity
Carbonic Anhydrase is one of the enzymes having highest Turn Over NO: at 36 million moles per minute. (bicarbonate)
More common NOs: are closer to 1000 moles/minute

7. Activity of Carbonic Anhydrase

8. Factors affecting the enzyme activity- the significance temperature and pH
Although Es speed up chemical reactions, each E works most efficiently under a specific set of conditions.
Because almost all Es are proteins, any factor that affects the shape of a protein, may affect E activity
High temperature and hostile pH are the major factors affecting the activity of the enzymes

9. Factors affecting enzyme activity the list of 5
These factors are :
Temperature
pH of the solution
Concentration of substrates and
that of enzymes
Activators or inhibitor molecules

10. Enzyme activity and temperature ↑es interaction B/w E and S
Temperature/heat is a sort of energy present in the particles that increases their activity or motion
Temperature ↑ the rate of reaction and activity of E and S so that both Can Interact with each other more frequently
It is more likely that the molecules of S will slot into active site of E leading to the formation of products

11. Effect of temperature on enzyme activity

12. High temperature leads to Denaturation temperature > 40C
Enzymes are proteins, ↑ of temperature above the optimum level (40 C) causes the protein to lose their :
3 D structure and folding and:
Breakage of bonds B/w the functional groups of AAs
Change of shape and loss of enzyme function
The optimum temperature for majority body enzymes is 37C°

13. Hostile temperature – Denaturation of E

14. ↑ in Substrate conc. ↑es Enzyme activity up to an optimum level
↑ of substrate ↑the enzyme activity up to an optimum level as more molecules of S have the chance to:
Bind with the active site of enzyme
Excess of S molecules, reduces the chances of finding an active site and no further ↑ in enzyme activity

15. ↑ substrate conc. ↑ enzyme activity up to optimum limit

16. ↑ in E conc.↑ E activity up to an optimum level
This effect is much like that of substrate
↑ in the enzyme conc. increases the rate of enzyme reaction up to an optimum level
Further ↑ in enzyme conc. has no effect on the reaction activity as no more S molecules are available
However, further ↑ in the substrate molecules, will certainly increase the rate of reaction

17. ↑ in E conc. increases E activity up to an optimum level

18. pH and activity of enzyme up to an optimum level
The pH level of a solution can also affects enzyme activity.
Many enzymes can only work within a narrow range ofpH
If an enzyme finds itself in a hostile pH range, it could becomes denatured.
The optimal pH for many enzymes is , but this is not always the case and may be variable

19. ↓ or↑ in pH – affects E activity Salivary and Gastric enzymes
Some enzymes, such as in the Gastric secretion work best at an acidic pH of 1.5, (Pepsin and Trypsin)
while others such as found in the Salivary and Intestinal secretions work best at a more alkaline pH of 8.0.
These include Lingual Lipase and Salivary Amylase in saliva
Amylase; Lipase, Protease and carboxy peptidase of pancreatic and Intestinal secretions

20. Enzyme activity - pH

21. Hostile pH and E activity – the mechanism S non covalent bonds with E
When a substrate slots into the active site of an enzyme
It forms temporary bonds (non covalent) with the groups at the active site (Amino acyl groups)
These groups are the functional groups of AA in the protein side chains and have important effects on :
the shape of enzyme

22. Hostile pH changes the shape of enzyme
If functional groups of AAs of the protein chain are in different order, the S would not bind temporary to the E
Because the shape of enzyme will be different
This is what happens when the pH changes when increased or decreased

23. Enzyme activity – the inhibition
Enzyme inhibition is the process when a chemical substance binds with the active site of an enzyme and:
Inhibits its activity so that active site is no more available to the substrates
Such substances are called enzyme inhibitors
These inhibitors can cause irreversible or reversible inhibition
Reversible inhibition can be competitive and non competitive