Lactoperoxidase immobilized

Figure 12.6 The immobilized glucose oxidase/lactoperoxidase system radioiodinates proteins through the intermediate formation of hydrogen peroxide from the oxidation of glucose. H2O2 then reacts with iodide anions to form reactive iodine (I2). This efficiently drives the formation of the highly reactive H2OI+ species that is capable of iodinating tyrosine or histidine residues (see Figure 12.2).

The iodination with lactoperoxidase is also very gentle and very often used Because the application of an enzyme for oxidation is more expensive than the use of common oxidation reagents, procedures involving immobilized lactoperoxidase have been worked out 21.22.26)... 

Commercial kits for protein labeling based on the application of immobilize lactoperoxidase have appeared recently (Fig. 2). For instance, lodo-beads of Pierce Eur[Pg.169]

Hemoproteins are a broad class of redox-proteins that act as cofactors, e.g. cytochrome c, or as biocatalysts, e.g. peroxidases. Direct ET between peroxidases such as horseradish peroxidase, lactoperoxidase," or chloropcroxidasc"" and electrode surfaces, mainly carbonaceous materials, were extensively studied. The mechanistic aspects related with the immobilized peroxidases on electrode surfaces and their utilization in developing biosensor devices were reviewed in detail. The direct electrical contact of peroxidases with electrodes was attributed to the location of the heme site at the exterior of the protein that yields close contact with the electrode surface even though the biocatalyst is randomly deposited on the electrode. For example, it was reported " that non-oriented randomly deposited horseradish peroxidase on a graphite electrode resulted in 40-50% of the adsorbed biocatalyst in an electrically contacted configuration. For other hemoproteins such as cytochrome c it was found that the surface modification of the electrodes with promoter units such as pyridine units induced the binding of the hemoproteins in an orientation that facilitated direct electron transfer. By this method, the promoter sites induce a binding-ET process-desorption mechanism at the modified electrode. Alternatively, the site-specific covalent attachment of hemoproteins such as cytochrome c resulted in the orientation of the protein on the electrode surfaces and direct ET communication. ... 

The separation of lactoperoxidase from the labeled protein may be avoided by using the immobilized enzyme (David and Reisfeld 1974). This technique applies immobilized lactoperoxidase together with glucose oxidase, which produces H2O2 in the presence of glucose. 

Amylases labelled with I have been prepared with the aid of immobilized lactoperoxidase. The catalytic activity of the labelled enzymes (measured against Phadebas starch) appeared to depend on the ratio of I to amylase. When the concentration of amylase in canine plasma was increased artificially, parallel curves were obtained for the disappearance of the label and a-amylase activity. 

Zhou, Y. Lim, L. T. (2009). Activation of Lactoperoxidase System in Milk by Glucose Oxidase Immobilized in Electrospim Polylactide Microfibers. Journal of Food Science, 74(2), C170-C176. 

---