Oxidation – reduction reactions
Oxidoreductase
Transference of an atom or group
between two molecules
Transferases
Hydrolysis reactions
Hydrolases
Removal of a group from a substrate (not by hydrolysis
Lyases
Isomerisation reactions
Isomerases
joining of two molecules
Ligases
Assumptions of Michaelis Menten equation
[S]0»»[E]0
The concentration of the intermediate [ES] attains a steady state value shortly after the start of the reaction
Michaelis Menton équation
Vm [S]/ Km + [S]
Disadvantage of Lineweaver Burke plot
Long extrapolation needed to determine Km
Restriction of enzyme mobility in a fixed spot
Enzyme immobilisation
Advantages of enzyme immobilisation
Catalyst reuse
Easier reactor operation
Easier product separation
Wider choice of reactor
Disadvantages of enzyme immobilisation
Loss or reduction in activity
Diffusional limitation
Additional cost
Factors for choosing supports
- Physical resistance to compression
- Hydrophilicity
- Inertness toward enzymes
- Biocompatibility
- Resistance to microbial attack
- Availablity at low cost
Physical enclosure of enzymes in a small space
Entrapment
Matrices used are polymetric materials
Matrix entrapment
Microcapsulation or trapped between thin, semi-permeable membranes
Membrane entrapment
Advantages of entrapment
- enzyme is retained
- no chemical modification/relatively stable forms
- easy handling and reusage
Disadvantages of entrapment
- Enzymes could leak into the solution
- Substrate need to diffuse in to access enzyme and product need to diffuse out
- If the conditions used in the polymerisation reaction are severe, it could lead to loss of enzyme activity
- Van der Waals
- -Hydrophobic-hydrophilic interactions
- Carriers: silica, carbon nanotubes, cellulose etc.
- Easy desorbed, simple and cheap, enzyme activity unaffected
Physical adsorption
- ionic bonds
- similar to physical adsorption
- carriers: polysaccharides and synthetic polymers with ion-exchange centers
ionic binding
- retention of the enzymes by covalent bonds
- carriers: polymers contain amino, carboxyl, sulfhydryl, hydroxyl, or phenolic groups
covalent binding
Is to cross link enzyme molecules with each other using agent such as glutaraldehyde
Features: similar to covalent bindings
Several methods are combined
Cross linking
stability of enzymes
enzyme half life
half life equation for first order reaction
t1/2 = ln 2/k
