Download Factors affecting the enzyme activity

Enzyme -3. Factors affecting enzyme activity
Lecture NO: 1st MBBS
Dr Muhammad Ramzan
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.
Michaelis-Menten equation
•
It is a set of mathematical expressions to calculate enzyme
activity in terms of speed of reaction from measurable
laboratory data.
Michaelis Menten equation
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
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
Activity of Carbonic Anhydrase
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
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
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
Effect of temperature on enzyme activity
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:
1
• Breakage of bonds B/w the functional groups of AAs
2
• Change of shape and loss of enzyme function
3
• The optimum temperature for majority body enzymes is 37C°
Hostile temperature – Denaturation of E
↑ 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
↑ substrate conc. ↑ enzyme activity
up to optimum limit
↑ 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
↑ in E conc. increases E activity
up to an optimum level
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 7.0-7.5, but this is not
always the case and may be variable
↓ 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
Enzyme activity - pH
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
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
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