Peroxidase lacto

Peroxidases (E.C. 1.11.1.7) are ubiquitously found in plants, microorganisms and animals. They are either named after their sources, for example, horseradish peroxidase and lacto- or myeloperoxidase, or akin to their substrates, such as cytochrome c, chloro- or lignin peroxidases. Most of the peroxidases studied so far are heme enzymes with ferric protoporphyrin IX (protoheme) as the prosthetic group (Fig. 1). However, the active centers of some peroxidases also contain selenium (glutathione peroxidase) [7], vanadium (bromoperoxidase)... 

Bjorck, L., Rosen, C., Marshall, V., and Reiter, B. (1975). Antibacterial activity of the lacto-peroxidase system in milk against pseudomonads and other gram-negative bacteria. Appl. Microbiol. 30, 199-204. 

Chance, B.C. (1949) The properties of the enzyme-substrate compounds of horse-radish and lacto -peroxidases, Science 109, 204-208. 

Iodination was explored further by Chandler et al. (1980) with lacto-peroxidase, which catalyzes iodination of Tyr with I. Further, they found that galactosyltransferase was inactivated by Al-acetylimidazole. This observation was consistent with an essential role of Tyr for activity. However, this reagent also affects the amino groups of Lys residues. Differentiation between these possibilities is afforded by the fact that deacetylation with hydroxylamine will occur for the Tyr derivative, but not for the Lys derivative. Since only about 40% of the activity could be recovered by deacetylation, Lys could also have been involved. Note that this indication is the second for the implication of a Lys residue with galactosyltransferase activity (see Powell and Brew, 1976c). 

Recently, application of lactoperoxidase-catalyzed iodination has taken precedence over non-enzymatic procedures. The enzyme-catalyzed reaction is reported to occur through the formation of an enzyme-substrate complex between the protein substrate and lacto-peroxidase. No detectable free I2 is formed by lactoperoxidase, and selectivity in attaining iodination of surface tyrosine residues in... 

In vitro studies on the ability of horseradish peroxidase or lacto-peroxidase to catalyze iodination of proteins at tyrosine residues are becoming quite frequent (244-248). The studies are designed either to provide better understanding of the incorporation of iodine into thyroid proteins or to develop better ways of producing radioactively labeled proteins for tracer studies. An immobilized enzyme system has been developed to achieve this second purpose (248). A large number of proteins incorporate iodine by this method which is superior to iodination with chloroamine-T or IC1. These iodinated proteins should prove invaluable in nutritional studies. 

It is known that superoxide reacts very slowly with all amino-acids since all rate constants are below 100 mol l 1 s (89). Hence its reactivity with proteins without prosthetic group is low (89). One exception seems to be collagen, in which proline residues are oxidized into hydroxyproline (90). On the other hand, superoxide reacts efficiently with free radicals such as tryptophanyl radical (91). Reaction is fast with metalloproteins. It proceeds mostly by oxidizing or reducing the metal center. Some characteristics and rate constants of reactions with metalloproteins are given in table 7. It is obvious that products are often unknown and that the mechanism is sometimes unclear. It seems that there is no reaction with transferrin (92) and horseradish and lacto-peroxidase compounds II (93). The reason is unknown. 

Both forms, however, contained intact RNA and the full complement of capsid polypeptides (50) Further evidence that a substantial conformational alteration of entero- and rhinovirus capsids accompanies the D to C antigenicity change has been obtained by examining the accessibilities of individual capsid proteins in intact virions, A-particles and naturally-occurring empty capsids to lacto-peroxidase-catalyzed iodination or alkylation with acetic anhydride (5I> 52). The results of these experiments are summarized in Table lY. Since under the experimental conditions employed the radioactive reagents formed covalent bonds with tyrosine residues... 

Active immobilized enzyme immobilized two-enzyme system for activation of the lacto-peroxidase system in milk... 

Glycoproteins have been located on the surface of two murine leukaemic cells, as shown by o-galactose oxidase-sodium borotridite and I-lacto-peroxidase-iodination techniques. The patterns on polyacrylamide gel electrophoresis of the solubilized glycoproteins from the two sources are indistinguishable but differ from those of the surface glycoproteins of HeLa cells. 

---