Please use this identifier to cite or link to this item: http://hdl.handle.net/1946/10202
Effect of chitosan on thermal stability of horseradish peroxidase
Chitin (β-1,4-linked N-acetyl-D-glucosamine) is, along with cellulose, nature’s most abundant organic polymer. Chitin is found in the cell walls of fungi and the shells of arthropods such as shrimp, crabs, krill, lobsters and insects. Chitosan (β-1,4-linked D-glucosamine) is the partially deacetylated derivative of chitin. Chitosan contains a free amine group that gives it different properties from chitin and cellulose. Two important properties of chitosan are degree of polymerisation (DP) and degree of deacetylation (DDA) which determine its behaviour in aqueous solutions. Carbodiimides mediate the formation of linkages between amines and carboxylates and can be used to form chitosan-protein conjugates. Chitosan affects thermal stability of proteins in aqueous solutions either as a co-solute or connected to the protein with a covalent bond.
Horseradish peroxidase (HRP) is an oxidoreductase whose main application is in biosensors and in waste water treatment. HRP can form a conjugate with chitosan by using carbodiimide and sulpho-N-hydroxysuccinimide (NHSS). Three different chitosan samples, two oligomers and one polymer were used to form conjugates with HRP and the thermal stability of the conjugates was studied. The effect of two different chitosan samples as co-solutes with the enzyme was also studied. Chitosan with degree of polymerisation of 4-8 proved to increase HRP’s thermal stability most. HRP’s half life at 65°C doubled after conjugation and the energy of deactivation of the enzyme was increased by 72%. As a cosolute the oligomer increased HRP’s half life at 65°C 3.6 fold at a concentration of 5% (w/v).