Lecture 3 - Enzyme Deactivation

Question 1

Name some environmental factors that could deactivate enzymes

Answer 1

pH, T, ionic strength, mechanical forces, detergents, solvents, heavy metals

Question 2

Derive the equation for half life of enzyme deactivation

Answer 2

Refer to notes
Start Ea ------ Ei
use vmax = K2Ea
End Vmax = VmaxoEXP(-Kdt)
Ln(2)/Kd

Question 3

Why would you want to immobilise an enzyme (4)

Answer 3

Immobilised enzymes are macroscopic particles that can be retained in the reactor

Separation is simplified

High volumetric productivities are possible

Immobilised enzymes are often more stable than soluble ones

Question 4

3 methods for immobilisation are?

Answer 4

Physical adsorption

Covelent bonding/ cross linking

Entrapment

Question 5

Discuss the adsorption immobilisation technique (3)

Answer 5

Expose enzyme in solution to the support allowing it to adsorb

Once immobilised the enzyme has lost its activity the enzyme can be stripped and replaced

It is possible to carry this process out without removing the support from the reactor

Question 6

What is covalent binding
What is the main advantage
comment on enzyme detachment and catalyst regeneration

Answer 6

Enzymes are poly-functional macromolecules

Enzymes can be coupled through reactive groups to a suitably activated surface

the main advantage of covalent methods in the strength of the binding

Enzyme detachment during use is usually negligible

Regeneration of the catalyst is not possible after deactivation

Question 7

What is physical retention
what does it utilise
What is the benefit

Answer 7

This involves entrapment of the enzyme in a semi permeable membrane or microcapsual

Entrapment utilises membranes with pores that are small enough to stop enzyme loss but not product or substrate loss

Remains in solution and any adverse effects resulting from adsorption or covalent methods are avoided

Question 8

Why is it important to know the kinetics of immobilised enzymes? (3)
Outline 3 effects and their significances

Answer 8

Enables prediction of how changes in operating conditions will affect reactor performance

Conformational effects
Electrostatic and partitioning effects
Diffusional, mass transfer effects

See notes

Question 9

Write the equation for the volumetric rate of reaction (Batch)

Answer 9

Michaelis menten

v = vmaxS/(S+km)

Question 10

Integrate the mass balance on a substrate to give a time dependant equation

Answer 10

slide 21

Question 11

Write down the batch equations for
Standard kinetics
Standard kinetics with mass transfer limitation
Standard kinetics with enzyme deactivation
Standard kinetics with mass transfer limitation and enzyme deactivation

Answer 11

slide 23

Question 12

What additives can be used to stabilise enzymes

Answer 12

Substrates, organic solvents and salts

the presence of a substrate can stabilise an active region

Question 13

What are conformational effects

Answer 13

The conformation (structure) of an enzyme may be altered by immobilisation

can not be quantified but can be measured

Question 14

What are electro static or partitioning effects

Answer 14

The concentration of the species (substrate product) in the immediate enzyme environment may be different form that in the bulk solution

Profound influence on activity

Question 15

What are diffusional, or mass transfer effects

Answer 15

Kinects of immobilised enzymes depend on the rate of substrate diffusion

Profound influence on activity